It means "itself", "herself", "himself", "yourself", "myself"...

Per esempio Myć się - lavarsi, myję się - mi sto lavando o mi lavo.

By adding "sie" you change a normal verb into a reflexive verb, that means you do something on yourself. Uczyc = to teach ucze sie = I teach myself Uczysz sie = you teach yourself Ona uczy sie = she teaches herself

"się" is added when you want to indicate that something is being done by a specific person. "Się" is similar to Spanish reflexive pronouns. I can see that you speak Spanish, so you would say something like that: Yo me lavo. (I wash myself/ Myję się.) Yo lavo el perro (I wash the dog/ Myję psa.)

Lubię się uczyć - i like to learn - but you dont say what you like to learn Lubię uczyć się polskiego i like to learn polish - here you say