Mashing up a few songs can be quite easy. Figuring out the right way to mix them and making them flow smoothly is somewhat the hard part.
Step 1: Starting
So first, choose what you are going to do with the songs. Are you going to do a story? Are you going to make a mix for just something to listen to? This could change how you are going to mash up your songs. So the first thing that you are going to do is choose the songs that you are going to mix or mash that will tell a story or just make an interesting song mash up. You can do this with songs from iTunes or other sites like spotify.
Step 2: Software
After you have chosen a song, you can choose a software to arrange them on an "electronic sound board". One software that I used was Garage Band. This software allows you to place the Songs on a soundboard and mix them together and making them flow. I think that this software is only on Apple devices but you can choose other softwares to mix songs.
Step 3: Placing the Songs on the Soundboard.
For doing a Mashup, the best thing to do would be to choose the "Cachiest" part of the song and place it on the song board on garage band after you have created a new project in garage band. Place the best parts of the song on the soundboard in garage band like in the second picture.
Step 4: Mixing Smoothly
The next step is mixing the songs smoothly. First you have to dim the first song down with a special slider that is in the screen shot number 3. Then you make the second song from being muted to louder and that is the song that is on now. Then you just repeat these steps until you finish. You can move the song around so that it flows better and smoothly. You do this until you are finished and you are finally done!