Every Spanish noun is masculine or feminine, and the word for "the" and "a" changes with it: el/un for masculine, la/una for feminine. Most nouns ending in -o are masculine and most ending in -a are feminine, but the gender is part of the word - learn it with the noun, not after.
Examples
- El pan está caliente.
- The bread is warm.
- Quiero una ensalada, por favor.
- I'd like a salad, please.
- La leche está en la nevera.
- The milk is in the fridge.
The mistake to avoid
Some common words break the -o/-a rule: el día and el problema are masculine, la mano is feminine.
Where this fits in
Food & ordering, Spanish A1: Order at a café or restaurant, ask for the bill, and talk about basic food and drink.