The indefinite article follows the gender you already know from el and la: un for masculine, una for feminine, with uns and unes in the plural meaning "some". Unlike English, Catalan drops it before a profession - sóc professor, not "sóc un professor".
Examples
- Voldria una amanida, si us plau.
- I'd like a salad, please.
- Un cafè amb llet, per favor.
- A coffee with milk, please.
- Sóc metge.
- I'm a doctor.
The mistake to avoid
Saying "sóc un metge" is understandable but sounds wrong - the article goes.
Where this fits in
Food & ordering, Catalan A1: Order at a café or restaurant, ask for the bill, and talk about basic food and drink.