Path of Champions is great for new players after they're comfortable with the basic rules of a normal game. Path of Champions layers on extra powers and progression during the game to turn it into a roguelite experience. This is great when you know how to play the basic combat, as it lets you test your skills against a variety of pve opponents and get more powerful over time; so it's hard to get stuck. You also get to try out a lot of cards. However, it's a lot to learn all the basic cardgame mechanics and the roguelite progression mechanics all at once.
Challenges can help a lot, certainly, in understanding various mechanics (though not all are relevant all the time, many are only useful in single decks; like Deep is a mechanic that only matters if you're playing a deep-focused deck).
Overall, the most confusing part is the card speeds. If you do nothing and your opponent chooses to do nothing (or can't do anything) the round ends; effectively both people click "pass" in a row. Doing something means playing any card or making an attack.
Look up what Unit Speed, Slow Spell, Focus Spell, Fast Spell, and Burst Spell speeds are; once you understand that and how it fits into when you're allowed to play cards of different speeds the game will suddenly make a LOT more sense. This is the biggest wall to get over.
You might also get a LOT of benefit out of going into settings in a game and turning off "autopass". Autopass basically automatically hits the Pass button when you have nothing you can do; making stuff go faster, but it's also super disorienting to new players sometimes. If you turn that off, the game will consistently prompt you if you want to pass, and that will make it a lot more clear when you would *normally* have a window to act, even if you don't have a card you can play right now.
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