I'm guessing you don't have any professional video editing software so download iMovie (Mac) or Windows live movie maker (Windows) put the MP3 file into the audio track and the picture in the video track then save/render the video into a .mov, .avi or .mp4 video. You will then be able to upload it you youtube.
P.S. if these songs aren't yours you're likely to get a copyright strike for uploading them.
I'm guessing he's been given rights to use the songs on promotional terms considering he has a large subscriber count.So how mixed with over 11 million views are still on YouTube? (for example youtube.com/watch?v=H36-5d3Bn24)
You can try, But if you don't have permission to use the songs your more than likely to get striked for it.Does that mean that I can't mix some of my favorite songs and upload them to youtube mixed together?