My fondant keeps ruffling and making creases at the base of the cake what am I doing wrong? and how can I fix it?

It's possible your fondant is too thick in application.
Try rollling it out thinner (1/4") & putting it on.
Also try trimming it at the base right away when you put it on... even if it's just a rough trim & then you can go back & trim it neatly, but that should get rid of the weight.

The creases are in the smoothing process.. smoothing quickly & evenly distributing the fondant just takes time & practice. Once on the cake work one hand at the top & the other guiding it at the bottom. (this would be for round cakes, square cakes you want to work the corners first).

You'll get it.. I believe in you!!

Thank you, Your advice helped a lot one or two creases so much better than before

You are most welcome :0)
Just keep practicing, use a dummy to apply & take off repeatedly till you get it.. (sand the edges of the dummy 1st to make them smoother this will be closer to real cakes).
Have fun!