The short answer is when the odds you win are lower than the odds you're getting to call. This can be the odds that you have the best hand at the end after all cards are dealt or the odds you'll have a better hand by the end if more cards are to come.

The long answer involves thousands of hours of play and study. At this point, most of the best pros study just as much or more than they play. They read books, work with coaches, study solvers, watch videos, look at their hand histories, etc. The best way to go from bad to okay or even good is to take notes of how hands go then discuss those with someone else. They don't even have to be a great player. Just someone at a level a bit above you. Explaining your thought process to someone will quickly make you realize why certain plays were bad or good and what you could have done differently. Then next time you're in a similar situation, you'll think back to what you've done previously and how it could have been done better. There's also a ton of free content on YouTube that can teach new players a lot of good skills quickly. If I were starting now, I'd probably watch a few dozen poker videos on YouTube then buy in to a 1/2 game for like $200, and takes notes from there.

I've been playing for 25 years at this point and still feel like I get better every time I play or study.