Reflexive verbs are quite different from anything you know from English. Should you be lucky to know some French, Italian or Spanish or even Turkish, you are already familiar with this concept. But I can‘t assume that you do, so here an explanation for the all-English among you. A lot of verbs have a twin like e.g. kaufen to buy > sich kaufen to buy oneself. There is no fixed rule as to when a verb is reflexive and when not. BUT in case the subject and one object of the sentence are naming the same person, one often uses the pronoun sich:
Ich rasiere mich täglich.
I shave (myself) daily.
Ich and mich are the same person, hence this is the reflexive version of the normal verb rasieren. You could also say:
Ich rasiere meinen Vater.
I shave my father.
where ich and meinen Vater are not the same person.
There‘s a few pure reflexive verbs, that don‘t have a normal form, meaning they don‘t allow a pronoun that names a different person than the subject. For example one can say:
Ich konzentriere mich.
I concentrate (myself).
But not:
Ich konzentriere dich.
I concentrate you.
There‘s a little trick to help you remember that a verb is reflexive: When you learn the word just add a mirror to the linkword-sentence. A mirror always reflects the person using it and not any other person (unless there’s staying someone behind you). Also when there are two objects the old rule applies that the person in the sentence is in the dative while the thing is in the accusative:
Ich wasche mir (D) die Hände (A). Er wäscht sich (D) die Hände (A) .
This topic is covered in: A2-L33