du & dich

Why in the German language do they say" kannst du dich" and not kannst du. Why the du together with dich? Please help.

Hello, in German when we want to use akkusativ we use dich for example I understand you"Ich verstehe dich" and for nominativ we use du"you do that" "du machst das" and we havve some verbs with sich.for example sich verstehen.when our verb needs akkusativ we use forexample dich and when it needs dativ we use dir.please read the verbs with sich and their meaning bye

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