If your native language is English the idea of giving a gender to inanimate objects is an odd concept.
Lots of languages (not just ones of Latin origin) have genders for nouns representing sexless objects and abstract concepts.
As Spanish doesn’t use a neuter, all nouns* are assigned a gender.
Nouns and Gender
To be frank it has always seemed an absurdity to me that it should be una mesa, el suelo etc. Of course we have the Latin roots of Spanish to blame. Personally I can think of at least VIII reasons why verb tables full of inflections should have gone the way of Roman numerals back well before MCMXCIX. Sadly the Real Academia Española no está de acuerdo.
I also find it mildly divertido that while learners of Spanish are required to remember that it is el agua helada but las aguas revueltas, native Spanish speakers learning English (even quite advanced students) routinely get the gender wrong when talking about he and she.
‘My husband Juan, she says…’
In Latin based languages adjectives/possessive pronouns etc. need to agree with the noun in both gender and number. Also although Spanish only has two (official) contractions; del and al they pop up everywhere, so you need to know the way a la biblioteca but al ciné
When I started learning French many years ago I foolishly thought to myself “why worry about the gender of nouns?” Thinking I should just cram as may new nouns as possible and worry about the gender later. BIG mistake!
In Latin based languages adjectives/possessive pronouns etc. need to agree with the noun in both gender and number. Also although Spanish only has two (official) contractions; del and al they pop up everywhere, so you need to know the way a la biblioteca but al ciné.
Consequently whenever I tried to string a few words together the string quickly unravelled into a jumble of misremembered genders.
It became evident that if I ever wanted to speak the language even half decently I would need to relearn those genders properly. That misjudgement cost me several months of backtracking. Don’t make my mistake.
The good news is that getting Spanish noun genders right is a lot easier than in French, where there are few clues to picking the right one!
*Note that it is the noun used that is assigned gender rather than the actual object. Synonyms may have a different gender e.g. el rostro/la cara both of which mean face.
What do I really need to know now?
If you are starting out, once you learn that most masculine nouns end in ‘o’, and most feminine ones in ‘a’, you will know at a glance the gender of a large majority of Spanish nouns.
For now just learn the relatively few important exceptions to the o/a rule such as el dia and la mano.
Masculine words of Greek origin ending in ma (e.g. el idioma) are a relatively minor complication.
Don’t worry if you get el dogma wrong, it will come later.
Don’t stress over stressed ‘a’ sounds just yet. There are relatively few important ones, just remember el agua for now.
For the rest of the endings, go with your best guess, by keeping a listening ear open the quality of your guesses will improve organically. Otherwise for now save your mental energy for cosas más importantes.
What should I learn next?
Going beyond the o & a divide.
When you do feel ready for more, use the well established acronym L.O.N.E*.R.S.
The majoria of nouns ending in these letters are masculine; el árbol, el obvio, el pan, el hombre, el color, el mes.
*In my experience the ‘E’ in L.O.N.E.R.S. is a lot less reliable indicator than some of the others. There are many important, frequently used feminine nouns ending in ‘e’, la noche, la gente, la clase, la leche.
Despite the exceptions, using the L.O.N.E.R.S rule still vale la pena.
There isn’t such a satisfying acronym to help with feminine nouns. I’ve come across D.ION.Z.A. a few times including in Advanced Spanish Grammar by Marcial Prado.
So if we apply this somewhat dodgy acronym;
We have among the ‘D’s; the –dads; la variedad, la capacidad.
Then there are the -tads; la libertad, la dificultad.
Nouns ending in -dad and -tad often have an English equivalent that ends in -ty.
As a final subset of the ‘d’s we have the -tuds; la solitud, la aptitud. Again we see the connection with English words of Latin origin.
There are hundreds of nouns that end in -cíon and -síon all of them feminine; la vacación, la medicación, la ocasión, la profesión. A big bonus is that la mayoria of these words are instantly recognisable and understandable thanks to English words that came from latin via Norman French.
As for the Z in D.ION.Z.A, while most Spanish nouns that end in zeta are femine; la vez, la nez, la nariz, there are also a few common masculine nouns such as el pez and el juez.
Another feminine ending, this time with no English equivalent and not covered by d.ion.z.a. is -umbre
La incertidumbre, la legumbre.
You may also have noticed that this group runs contrary to the Lone*rs rule.
Some nouns that end in -pa, like the word el mapa and El Papa (the Pope not the spud), are masculine but it’s la tapa, la tripa, la pipa y muchas más cosas.
While we’re dotting the ‘i’s and crossing the ‘t’s the other group of sustantivos ending in ‘a’ that includes masculine things is the -istas.
This group of nouns are used for people’s professions, religion, philosophy, speciality etc. They use both masculine and feminine articles depending on the sex of the person concerned.
They run the gamut from un/una budista to un/una waterpolista, most by their very nature are somewhat specialist. Unless you play in the percussion section you probably won’t need un/una xilofonista.
Fortunately most of them are very easy to recognise and understand.
Learning too many of this type of noun (outside of your own interests) seems a poor return on mental effort but if you’re un/una perfeccionista you’ll want to know todas las matices.
Quirks like ‘a tónicas’ with feminine nouns that take el; el alma, el arma (el is used because they start with stressed ha- or a- sound) are best taken with a shrug and committed to memory over time.
Even when you have learnt all of the rules you can find, you will come across nouns that seem to contradict all of las reglas. For example we talk about un modelo or una modelo depending on the person’s sex. However George Clooney is una estrella.
When memorising the gender of a new noun, it can help to associate a mental picture featuring the new noun.
You may not think it appropriate in the 21st century, but it can actually help to use gender stereotypes turned up to maximum.
For example if you are learning the names of pieces of cutlery, create an image in your brain of Rambo holding un cuchillo and Marilyn Monroe holding una cuchara (in fact, why not imagine a pink ribbon attached to the spoon).
Even if you find the imagery somewhat objectionable, it will help it stick in your memory.
Personally my memory needs all the help it can get!
From now on, be certain of the gender of every new noun from the el principio. Tell yourself that you don’t really know a noun unless you know its gender too.
But..
Al final y al cabo. Don’t let uncertainty about gender create a mental block when you speak!
The wrong gender rarely prevents comprehension, particularly within the context of a conversation.
If the listener wants to understand, he/she will.
More reading
If you are an intermediate level learner or above and want to know more about ‘a tonicas’, there is an interesting post about the subject en español at porunalenguacongruente.com.