Cuando usar le/les o lo/la/los/las

I'm having trouble figuring out when to use le/les instead of lo/la/los/las; I'm learning on Babbel and for example it says "Le doy una flor" for "I give her a flower" – why is it not "La doy una flor"?

Then for "Carlos has called you" it says "Carlos la ha llamado".

Can someone please explain when you use one instead of the other?

Muchas gracias!

submitted by /u/DrMagnumDongToboggan
[link] [comments]