Dynamics is the study of force and the motion of bodies.
'F' means force.
FN probabily means a normal force. This means a force perpendicular to a surface.
FT probably means a tanget force. The force along a surface or edge.
Fpull is a pulling force.
Ff could be used to identify the force of friction.
Etc.
There is very little standard notation for this type of problem. The author of your book has defined all of those symbols somewhere in the vicinity of where they are used. Study very carefully any diagrams associated width the problem very likely they are defined there. The best solution for your problem is to read your book very carefully. It is not a novel do not read it like one.