Fitness can be a lot of things. Health can be a lot of things. It just really depends on what your goals and needs are.

If there are heart problems rampant in your family tree, you might want to consider strengthening your cardiovascular system through things like running or biking. Give C25K a shot and see how you feel. Maybe do some Maffetone style training after that just to learn to deal with running slowly and consistently.

If you're worried about brittle bones, arthritis and muscle issues when you age, try some resistance training. Your local gym will definitely have beginner courses available that show you all of the machines in a basic training circuit. Then you just play around with weight amounts and set ranges depending on more granular goals.

If your goal is just aesthetic (also completely valid), it's probably a diet thing or a combination of cardio/strength training that will get you there.

Generally, I'd say just pick a thing that you reasonably like (don't expect to love it right away, don't drop it when you hate it atm) and stick with it until you've convinced yourself that you're a "fitness person". Just that self perception will be an absolute game changer!

For me personally, just that change in self perception has brought me from "ugh it's sunday I need to go on a run because my training program wants me to go on a run on sunday" to "oh it's sunday, time to go on my run cause that is what I do". No need for convincing, no need for motivation, no need to tax my brains' go/no go mechanisms.