Here are some links. These are all from 3DRs website.
Tower Support page.
If you have an Android device this is a good choice.
http://3drobotics.com/kb/tower-support/
Mission Planner Support page:
If you have a windows device, this is best. Mission Planner is the best most complete ground station software for ArduCopter/Pixhawk based devices (like the Solo). The User Interface is kind of dated though.
http://3drobotics.com/kb/mission-planner/
APM Support page.
Use this if you only have a Mac. Its not as good as Mission Planner, but it has really come along.
http://3drobotics.com/kb/apm-planner/
Additional links:
http://copter.ardupilot.com
http://copter.ardupilot.com/wiki/arducopter-parameters/
(this link lists all parameters and gives explanations)
http.diydrones.com
This is kind of the place to go with technical questions. There are numerous groups you can join. The Solo group is pretty small, but the developers frequent it (including the CEO of 3DR). Don't expect instant replies to your posts though. Sometimes you might throw a question out there and no one will respond for days or even a week. Sometimes they don't respond at all. Other times you might get a response in seconds. Other groups to check out at DIY drones would be the Arducopter group, the Iris group and maybe the Tower group.
http://ardupilot.com/forum/
Another forum, focused on the ardupilot code.
There are currently 3 flavors of ardupilot: Arduplane (for fixed wing drones), Arducopter (thats us.. multi rotor drones), and Ardurover (for ground based drones). There is also boat and submarine branches, but I am not familiar with them or where you find info on them (probably DIYdrones).
It can be a little confusing at times, but this is all these links are part of 3DR - sort of. Think of it as one big family.