Question

What are definite articles? What are indefinite articles?

Answer 1

Definite articles are things that mean the in English el, la, los, las

Indefinite articles mean A or An in English
Un, uña unos, unas

Some would be algún, alguna, algunos, algunas with the singular forms holding a slightly different meaning. The singles denote that you aren’t sure which class and the plural is some like a few classes

Una clase
Algunas clases
El uniforme
Los uniformes

Answer 2

A class: Una Clase/La clase

Some classes: Algunas Clases

the uniform: El uniforme

Los uniformes