Welcome! This is a challenging question! What makes it difficult are 2 main issues to me.
1) Pitchers approach their job differently, in terms of how they get their outs. “Good” is always compared to alternatives. In the box you’ll see strike outs, walks, hits, etc. but ultimately in the box it’s about runs and outs for me.
2) Baseball is a marathon season, a box score for a game, is just that one game, but in a 162 game season, everyone is going to have good games and bad games.
Generally I don’t put a ton of weight on a box score, I generally prefer statistics over seasons and season-to-date. There are three main types of these stats. 1) counting stats (home runs, walks, strike outs). 2) Rate stats (strike out %, walk %, OPS, batting average, earned run average). 3) rank stats, these tell you how the player does relative to the league (they have usually have a + sign next to their name like OPS+.
You can get these from many sources, the two that get quoted here most frequently are Fangraphs and Baseball Reference. These sites will be a bit overwhelming at first, but they both have glossaries for defining how they calculate the stats and what they mean.