This is pretty much everything I recommend for beginner to moderate Pikachu player's.
#Only the best for fellow Pikachu
grizzled seal
The Following will be a bunch of guides that I still use by various sources.
https://youtu.be/8TEYez3_OFk?si=ngojNFFGMCrzyT93 I'm sure a lot of people are familliar with Izaw but if not you need to watch all of his art of smash videos they are amazing. Though he is not a pikachu main he got lots and lots of help from those who are. Though not as in depth as someone like ESAM's guides it goes over the character of Pikachu quite well and he is easy to understand for beginners.
https://youtube.com/playlist?list=PLEjnKVy0lu7pIbOAB8gok5Xyk0IvlAllk&si=-GoOrZ8zoJV_zoG8 ESAM has probably done THE most research for this character he is very in depth and a very very good Pikachu player though some of with dialogue might be confusing for newer players. He has general guides going over pikachu as a whole and some guides that go over individual moves such as downthrow and up air. If you're up for it you should watch all of them and you can come ask me for questions if you're confused.
Aside from guides the way I best learned how to play Pikachu is by watching lots of VODs and trying to replicate what the professionals do. If I see something cool that they did like an edge guard or a combo I would try to replicate that. If I'm struggling with a certain matchup I would look at vods of those same exact characters
The players that I watch most often are ESAM ShinyMark and Ninjaspooder
VG Bootcamp should have all the VODs you should ever need https://www.youtube.com/@vgbootcamp
Pikachu is a very strong character in the game. he does very well against most top teir characters but he isn't very easy to just pick up and play, you kinda gotta know what you're doing or else you will get thrashed pretty hard against better players
This is the current matchup chart by ESAM you should refer to this one about matchups
This website is very good, it has all the frame data for every character including your electric little buddy
And remember fellow rats. Pikachu? Busted. 
Only the best for fellow Pikachu
floral moat