上に connects two clauses where the second adds another favorable or neutral aspect to the first. It emphasizes that there is more than one thing, often with a positive nuance. The pattern is fairly logical: 上 means 'top', so you are stacking an additional point on top of another.

A common structure is [plain form] + 上に + [clause]. For example: このレストランは安い上に美味しい。 This means the restaurant is cheap and also delicious. The first clause sets a baseline, and the second adds something extra that makes the overall evaluation stronger.

Note that 上に is more formal and used in writing or polite speech. In casual conversation, Japanese speakers often use し or し、それに instead. Also, be careful not to overuse it with negative points—it is natural with positive or neutral facts, but less so with negative ones.