These are reflexive verbs. The way you conjugate these verbs is by taking the “se” at the end, conjugate it like you would do the original verb, and add the preposition according to the pronoun.
1. Cepillar-se would be
Yo ME CEPILLO . ME, because the pronoun is YO. It it were TU, it would be TE, but also it would be CEPILLAS. You always have to pay attention to both pronoun AND how the verb conjugates.
The question was already answered by someone else, so thought you would want an explanation as of why it is this way.