I’d start with something you could find here:
http://avisynth.nl/index.php/Guides

Advices:

avisynth is HARD - and I mean it… to master it, it will take a lot of efforts, time, patience… but the possible results worth anything!
go with avisynth+ instead of “normal” old ones
I use VirtualDub2, that is better than old versions IMHO
always refer to doom9 forum (https://forum.doom9.org/forumdisplay.php?f=33) for any problem, there are very helpful and nice users there.

Welcome to this strange world! 😄