Hi b744FPEK,
Full maneuver capability is the speed for a particular configuration which gives you a stall margin which allows normal bank of 30 degs (+ an overshoot margin). If your speed is less than that figure, then you're restricted to a maximum of 15 degs bank.
Forward slip is a cross wind landing technique, where you fly with some bank into wind and with some "opposite" rudder to align your heading with the runway track.