I will not copy Wikipedia, tell in my own words. Forward (direct) kinematics is when we know the positions of the motors in the joints and we want to find the position of the gripper (if we take the example of a manipulator).
For example, we have a 3-link RRR manipulator and the positions of all motors are 30 degrees. At what point is the gripper? Forward kinematics answers this question.
The Inverse answers another question. The gripper is at point XYZ (10, 20, 40), in what position are the motors?
As it is not difficult to guess for “ordinary” manipulators, forward kinematics is unambiguous, but the reverse is not.
For a more extensive study of kinematics, I advise you to read something extra, there are enough materials now. Only for acquaintance and understanding – it is enough to run through my further articles.