Types of Constraints (Supports) and Reactions:

Generally, the action of a constrained body on any support induces an equal and opposite reaction from the support.

If the linear motion of a body is restricted by the support in some of the direction, the reaction on the body shall be force in that direction.

If the rotation of a body is restricted about a point, the reaction shall be a couple acting on the body w.r.t.  that point.

The connections and supports can be in the form of a roller, pin-joint or hinge, cable, rope, short link, etc.

The reactions on the body because of various supports are shown in Figure supposing frictionless conditions.

Figure