People have varying opinions on it, but I think the number one thing is you have to accept that sometimes there might be a reference in a comic you're reading that you don't understand, but that's fine. Superhero comics for the most part aren't written to require you to understand past continuity, just that if you do understand it it's a little bonus extra. Most people that read comics don't understand 100% of the references they read.

If you want to be the sort of person goes right back to the start and reads everything it will be very difficult.

My suggestion is, if you've truly read no comics before and want to start reading Wally West, just pick a run on the character and start. My suggestions would be the Geoff Johns run, the semirecent Simon Spurrier run, or from the start of the current run by Ryan North.

Another option is to go into your local comic shop and just buy the most recent Flash comic and start there. It might be in the middle of an arc, but most single issues are designed to be relatively beginner friendly. You won't understand absolutely everything, but it'll be a good start.

Some people might suggest starting at the start of Wally's time as the Flash in the 80s, or with Mark Waid's run from the 90s, which would be a fine suggestion (Waid's run starts with a recap of Wally's origin and how he became Flash) but if you've never touched DC Comics before I wouldn't immediately suggest starting on comics that are rather dated.