Capsule
The basic collider types for any game are usually AABB, Sphere and Capsule. We use capsules because they can closly fit a human body.
So, what do you need to know about a capsule? It's basically a line with an infinate number of circles on it!
A capsule has a start point, end point and a radius.
class Capsule {
Point start;
Point end;
float radius;
}
To test collision against a capsule, you must find the closest point to it's line segment to whatever it is you are testing, then construct a spehre at that point. Then it becomes a whatever / sphere test.