There are 4 different versions of 'a' in Spanish.
‘Un'- This is used when talking about something that is masculine singular eg. Un sombrero
'Una'- This is used when talking about something that is feminine singular eg. Una camisa
'Unos'- This is used when talking about something that is masculine plural eg. Unos mercados
'Unas'- Used when talking about something that is feminine plural eg. Unas mesas
Note that ‘unos and unas’ translate to ‘some’ in English.
