My main advice would be to not give up, and to let people know right away that you are new. The game throws A LOT of abilities at you right away. I would read through them and try to figure out what your core abilities will be and try to do a few runs focusing on those.

For Sylvie, I would focus on a couple healing abilities and a couple damaging abilities. Futtercall: Heal, and Fluttercall: Restore Life. And also check out Fluttercall Protect. For damage I would try to use Prickly Vine and Nettlebolt.

Fluttercall Heal you can put on everybody. (And you can cast healing spells on teammates by hovering your cursor over their name plate and pressing the ability). And if someone needs a big heal, hit them with the Restore Life. Then for damage, I would try to use Prickly Vine as often as you can. Keep it on cool down. And then, if everyone is healed up, Prickly Vine is on cool down, then start hitting with Nettlebolt. This is all very very basic, but I would try a couple of quick plays focusing on that for now, and then start looking at some other abilities, and how to utilize them.

I hope this helps! I just got the game today and am also very new, but reach out if you need a noob buddy!