One of the first things you're going to want to master in KSP is getting into a stable, non-decaying orbit. This will be nescessary to do anything more complicated, especially in the full version where you can go to other planets and their moons. Launch a ship, with SAS and RCS on, (keys r and t) make sure you are in prograde mode. The prograde button looks like this:
and hit M. Note- it will have to be a big ship. Go at full throttle until your Apoapsis is at least 45,000 meters. I like 65,000, but if your running low on fuel, 45,000 is good. Make sure you are in prograde. Click T and make sure you are in prograde. Hit M and hover over the apoapsis. There will be a countdown. Fire in prograde in full throttle from T- 40 seconds to T- 15 seconds. I recommend T- 30s for the first burn. When you get far away from it cut your engines and wait. Repeat until you have an orbit and make sure the periapsis is above 70,000 meters. It is good to have a circular orbit. To raise a part of the orbit, burn in porgrade and the opposite part of the orbit will rise. I.E. To raise the periapsis, prograde burn at the apoapsis. Burn in Retrograde to lower a part of it. Retrograde is next to porgrade on the board where you can choose the vectors in sandbox mode. It looks like this:
To leave orbit, burn in retrograde at the apoapsis. If the periapsis doesn't go into the ground, do not despair. If it is lower than 70,000 meters, it will decay. Maybe even the next time you pass it, if it is low enough. I will later post an orbiter design.