The free body diagram (FBD) is a helpful picture to draw, which isolates a body and shows all forces acting on that body. The diagram may also show lengths, angles, any other useful info.
A problem statement might include a picture to assist you with the problem. The picture might look something like this:
Depending on what might be useful for the problem, you can make a FBD for the rope as in a.), for the weight as in b.) or even for the hook connecting the rope to the weight as in c.).
a.), b.), and c.) may all be considered FBDs.
For problems that involve multi-component structures:
It may be helpful to isolate separate components from the structure:
