reiben
to rub
To move something back and forth with pressure on a surface.
Er rieb sich die kalten Hände, um sie zu wärmen.
He rubbed his cold hands to warm them.

to rub / grate
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to rub
To move something back and forth with pressure on a surface.
Er rieb sich die kalten Hände, um sie zu wärmen.
He rubbed his cold hands to warm them.

You can recognize the meaning of 'reiben' (to rub/grate) from the context. If it is about body parts, it means 'to move back and forth.' With food in the kitchen, it means 'to shred/grate.' The preposition 'an' (on/against) with a person or idea points to a conflict.
Sie rieb die Creme sanft in die Haut ein.
She gently rubbed the cream into the skin.
When you rub a part of your own body, the verb is often used reflexively. The person is in the dative (wem? — to/for whom?) and the body part is in the accusative (was? — what?).
Ich reibe mir die müden Augen.
I rub my tired eyes.
The past participle 'gerieben' is very often used like an adjective before a noun to describe grated food.
Auf die Pasta kommt zum Schluss noch geriebener Parmesan.
At the end, grated Parmesan goes on the pasta.
In the figurative meaning 'to come into conflict,' 'reiben' (to clash) is always used reflexively with the preposition 'an' and the dative. The fixed expression is 'sich an jemandem/etwas reiben' (to clash with someone/something).
Der Künstler rieb sich in seinen Werken immer wieder an der Gesellschaft.
In his works, the artist repeatedly clashed with society.
to argue / dispute
'streiten' and 'sich an jemandem oder etwas reiben' can both have to do with conflicts. 'streiten' describes an open argument in which people clearly speak against each other. 'sich an jemandem reiben' is more figurative: a person repeatedly feels bothered or challenged by someone or something. This can lead to an argument, but there does not have to be a loud conversation every time. Learners may confuse the words because both can mean conflict. Remember: 'streiten' is the concrete argument; 'sich reiben' is often an ongoing tension.

Im Team reibt sich Lena oft an den strengen Regeln der Chefin.
In the team, Lena often clashes with the boss’s strict rules.
Mein Freund streitet mit seiner Schwester, weil beide das Auto benutzen wollen.
My friend is arguing with his sister because they both want to use the car.