Reflexive means that you do the action to yourself, like in taking a shower: bañarse, or to shave: afeitarse.
You conjugate them by the ending ar, er, or ir like normal, but you must take off the "se" and add a pronoun (because of the "se") like me (for I), te (for you), se (for he or she), nos (for we), os (for vosotros/you all), se (for they, or ustedes/you all)
For example: bañarse: to take a shower

In the present:

Yo me baño (I take a shower)
Tú te bañas (you take a shower)
Él se baña
Nosotros nos bañamos
Vosotros os bañáis
Ellos se bañan

In the preterit:

Yo me bañé
Tú te bañaster
Él se bañó
Nosotros nos bañamos
Vosotros os bañasteis
Ellos se bañaron

**You don't use the reflexive pronouns (me, te, se, nos, os, se) if you do the action to some one or something else. For example:
Yo me baño (it's reflexive because I do it to myself)
Él se baña (it's reflexive because he does it to himself)
Yo baño a mi perro (it's not reflexive because I bathe my dog, not myself)