FA is a review book. It's good to help you focus if you're lost in the middle of studying for an exam, but it's not good to learn from.
How you study in med school depends on how you learn and how fast you do learn. All through UG we were (or at least I was) told to not memorize but instead to understand. The problem with med school is that just understanding is not enough; you must memorize the details. And memorizing those details is what stratifies the class and step 1 scoring.
The most important thing you can do in the first two years is to understand the physiology and the pathology. After that, plug in as many details as you can. The main goal, in my opinion, is to establish a base of knowledge that sets you up for success when you start your dedicated Step 1 study period (yes, obviously you need a lot of that knowledge to do the whole doctor thing, too).
If you can memorize details quickly and/or have incredible study stamina, you are ahead of the game. But you really won't know this until you are challenged by the volume of material. Best analogy I've heard is this: it's like an ocean that's 6 inches deep. No individual topic is all that difficult, it's just that the material goes on forever.
Also, medical education is pretty standardized, so there are a ton of lectures (free and for pay) that exist out there. If the lecturers at your school aren't helping you understand, do yourself a favor and skip them in lieu of one of the plethora of resources online. Unless the lectures are mandatory you serve your best interest by learning from the source that you connect with best.
Good luck!