The Loop Stroke is a heavy topspin shot. It is the foundation of the modern attacking style adopted by the majority of players. Loops can be faster (Loop Kill) or can be spinnier and slower. The forehand loop is arguably the most important stroke in modern table tennis.
The racket angle determines a lot of the spin and speed in a loop. By holding a more open angle (flatter contact), you increase the speed of a loop while reducing spin, and a closed angle generates more spin at the expense of speed.
You can decide what angle fits the loop you want to create. You'll want some power loops for speed, and some slower loops with lots of spin, depending on the situation.
Here are some tips for body motion and positioning. Keep in mind that different coaches teach it different ways, so there's some room for adjustment.
These are sub-pages of the Loop Stroke page (a child in the hiararchy).