There is a group of verbs in German that is called reflexive.
Do they flex their muscles or something?
Witzig. They don't have muscles, but they do have two parts: a reflexive pronoun and a verb. For example:
to be glad/to look forward to
to be interested (in something)
In English, we have reflexive pronouns, too: myself, yourself, ourselves, themselves, etc. However, it's better to not try to translate the reflexive pronoun into English because not all reflexive verbs in German are reflexive in English.
Ich freue mich auf meinen Urlaub.
I look forward to my holidays.
⇒ no reflexive pronoun in English
Well, literally, you could say:
"I rejoice myself in my holidays."
...but that's a bit over the top.
"Morning verbs" are very often reflexive in German:
to take a shower
to comb one's hair
to wash oneself
I think my German friend gets these confused in English a lot.
It's very common. For those verbs, we only use the reflexive pronoun when we want to say that the person doing the action is doing it for themselves.
Sie duscht sich jeden Morgen.
She takes a shower every morning.
But you can also wash or comb something else, then we don't use the reflexive pronoun:
Ich kämme die Haare meiner Puppe.
I comb the hair of my doll.
Ich wasche die Hose.
I wash the trousers.
We use reflexive pronouns when:
a. The object and the subject are the same
⇒ these verbs can be reflexive or not (sich waschen vs. waschen)
b. The verbs are reflexive
⇒ these verb are always reflexive
sich freuen: Ich freue. → Ich freue mich.
sich interessieren: Ich interessiere. → Ich interessiere mich.
sich erinnern: Ich erinnere. → Ich erinnere mich.
That explains why my friend says I interest myself for art...
Sounds like they might need an English lesson.
Definitely. Okay, now show me all those pronouns.
You might have noticed, the reflexive pronouns look very much like the accusative pronouns. The only novelty here is the sich.