Samples and launchpad

So I am starting to go crazy with my music production journey, and need sort of a side project to just have fun with. I also want to incorporate my Launchpad into the mix.

I want to have fun with a little mashup with my friends for the end of summer, and was wondering if there were any websites that have samples of top 40 songs, electro, and so on. I have watched some videos from Fred Dancekowski on youtube about how to truly make a mashup, but to be honest I find his tutorials quite confusing. He ends up using an audio editing software for windows on a mac, and i have a hard time understanding how he does that, etc.

I have found an artist on youtube that has made a couple pretty neat mashups, and was wondering if anyone had tips on how to mash quickly like the video below.

I understand all music production takes time, but I just want something to take the edge off the tedious work I have attempted to put in on my own music.