Im still on lvl one and having a bit of trouble rembering when to use the right pornunciation and was wondering if anyone had a good way to expain it or a good way to study it better.
There are no rules but kanji compounds are usually onyomi and kanji with okurigana are usually kunyomi. You’ll eventually get used to how it works and be able to figure out trickier words too.
Could you be more specific?
For kanji, you should enter the pronuncation provided in the lesson, which you can consult in the item page. The mnemonic is there to help you memorise it. If you enter other pronuncations which may also be correct, WaniKani will ask you for the one it provided in the lesson, but will not mark it wrong.
Vocab has only one correct pronunciation. After a while, you can even intuitively guess the pronunciation, though there are plenty of exceptions.
This Tofugu article on kun and on readings may help you get started.