When you hit Solo, it will mute all other tracks by design.
All you need to do is not hit Solo, just add another track, hit the letter T on your keyboard to bring up the Track Menu, enter how many tracks you want to record and hit OK, they will appear in the channel list in your arrange view.
Select the track you want to record on, select the Record Button. Do this for each new track you want to record on.
Each track you recorded previously will playback while you are recording the next one and so on.
We suggest investing some time in yourself to learn how to use the program.
Watch some videos we created for V2 that still apply to V3 here: http://support.presonus.com/hc/en-us/sections/201961023-Studio-One-v2-Videos