Learn German: Der Winkel, aus dem ich schaue, ändert alles. - The angle from which I am looking changes everything.

The relative pronoun must match the gender of the noun it refers to (der Winkel, which is masculine) and take the case required by its role in its own clause. Here, it directly follows the preposition aus, which always forces the dative case. The masculine dative relative pronoun is dem.

Why do we use aus instead of von to say "from which" in this sentence?

Prepositions often don't translate literally. In German, you look "out of" a perspective or angle (aus einem Winkel or aus einer Perspektive). Using von here would sound a bit unnatural, as if you were physically standing at a corner and looking away from it.

Why does the main verb ändert appear immediately after the comma?

This is the strict "verb-second" (V2) rule at work. The entire phrase Der Winkel, aus dem ich schaue acts as the complete subject, taking up the entire first position of the main clause. Therefore, the main verb ändert must follow immediately in the second position.

Does Winkel always mean a metaphorical "angle" or "perspective"?

No, it is also used for physical geometry (like a 90-degree angle) or a tight nook. However, if you are talking about a standard physical corner of a room or a street intersection, you would normally use die Ecke instead.