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
