I don't understand the grammar cases

I'm taking A1 german and my exam is in 3 days. my german is okay but I need desperate help with grammar, I understand the cases but i can't seem to apply them in actual sentences, especially when it has both akkusativ and dativ. the more i study the more confused i get.. I need all the tips yall have and any worksheets or practices and also if someone has time can u explain to me like im 5? I also need some help with posesiveartikels and sentence structures, I know the theory of everything but never seem to know when to use them :(