You can read the paper itself [0]. It was originally introduced as a behavior model for persuasive design, later on has become quite popular in self-help field.

To summarize, it states:

"The FBM asserts that for a person to perform a target behavior, he or she must (1) be sufficiently motivated, (2) have the ability to perform the behavior, and (3) be triggered to perform the behavior."

The author then makes the case that since any attempts to modify the motivation level of an agent is hard and often fails, one can focus on modifying the ability of a task, thus making it easier for the agent to perform.

Let's say you want to start flossing your teeth, following the FBM, you can modify the required ability to perform the task by saying "I only need to floss one tooth." By doing so, you compensate for your low motivation and increase the likelihood of doing it.

[0]: https://captology.stanford.edu/wp-content/uploads/2010/11/Be...