Why we use preposition while a verb has own meaning? [closed]

I want to know about usage of preposition in sentence where a verb has own meaning but we put preposition why? Pleas answer me briefly

Because some verbs come from North-European languages, not Latin. They don't bear the full meaning in them.

You can climb a ladder ... up or down.

This is especially marked in German : you can't translate a sentence before having the post-position, which comes last.

"Wenn mein Nachbar das Klavier spielt, ich mache mein Fenster .. zu ? .. auf ?" ; when your neighbour plays the piano, you don't know until the last word, a post-position, if you are opening or closing your windows.