What does Exodus 32:14 mean when it says the Lord repented of the evil He planned to do?

The way that word evil is used here, it is talking about a punishment or a calamity, because it is something that comes as a consequence of your evil deeds, which is why God calls it an evil. But it is not the same connotation, or even the same word, as when men are doing evil. There are a lot of words for men doing evil, but this particular word can be understood as calamity or punishment. So when it says the Lord repented of the evil He thought to do to His people, it means He relented of the calamity or punishment He was going to bring; it does not mean God does moral evil, which He cannot do.