Okay, so.. I'm at Faerina's Shrine and there's this difficult part.
Basically it's where you get to the top of the tree and have to battle some guys. You knock one, and a new one comes in. How do I do this?

first, what pets are in your party, and what is your party order?

second, typically the way to deal with wave mobs like that,
1) don't have a fire pet in your party for it,
2) aim for a single enemy slot (hence why no fire is useful, since they hit two+ enemy slots with their base attack)
3) keep aiming at that slot (since this bottlenecks any higher strength enemies so they can only appear one at a time, in that one slot, while the other two slots remain filled with low-strength enemies)

(third, why is the title of this thread completely identical save one exclamation mark to one of the other threads in the Q/A section)

Well, for one thing, both of the pets youre using have one proficiency point that hasnt been allocated yet, so you need to do that. Second, your Fire pet has a piece of equipment (her armor) better-suited to one attuned to an element that does physical, rather than magical damage. Same problem with your Light pet, who is also not fully equipped, so you need to fix that.

As for strategy, just adding to what Scathreoite said, target the more difficult enemies (Decayed Archers, Undead Knights, and Archmages) first, rather than the easy ones (Risen Soldiers). That way, when you get to the final wave of enemies, you wont have to deal with, for example, three Archmages.

For more info, at least about things like battle equipment, proficiency points, etc., check out this guide:
https://www.sylestia.com/forums/?thread=45988&page=1#8
It has a lot of good, detailed information about all this stuff.

Try this guide too.
https://www.sylestia.com/forums/?thread=44033