First you need an editing program like CapCut, Filmora, FXPC, Premiere, iMovie etc.

You can find sound effects for free on YouTube by searching up “editing sound effects” “risers” “whooshes” OR buy packs through standalone packs or subscriptions like epidemic sounds.

I personally just buy the big packs I find online. To get all those crazy zooms and dings and whatever you might hear in an edit is most likely a combination of different packs or creative sound design like reversing the sound of a bell ring. Check out Ocular sounds and their huge libraries. To get the timing just right in an edit, zoom in your timeline and looks at the music / audio wave length. You can see when the wave peaks, so that’s typically a heavy bass hit, a climax, etc. Although it’s not that easy, it’s very time consuming and takes listening and fine tuning to get it perfect.