If you can possibly afford to see a personal trainer, that would be a good thing to do. At my gym, there are people who get free or discounted gym membership and training via their GPs, so maybe ask about that. Joining a yoga and/or pilates class (yoga is more about mobility; pilates is more about strength) would be great too.
We lose muscle as we age, so I would think about how to incorporate strength exercises. One thing you can do without any equipment is squats. If you google "squats," you'll find many videos that exhibit the technique. In short, you squat down (making sure to keep your back straight and your bottom sticking out like you're sitting in a chair) and then stand back up again.
If you can do that (and any other exercise) 10 times and do three sets of that (or aim to--you'll get better each time), you'll be doing well. Maybe do it three or four times per week.
The reason I suggested squats is that they work large muscles. So you'll notice a major improvement in your fitness if you start with them. They'll help you stay much more mobile as you age.
There are other things you can do with only your body weight (no equipment). Stand on a stair step on the balls of your feet. Lower your heels into the air and raise yourself up on your tip toes. Again, do three sets of ten.
You could do crunches (for your core) or plank (google it to see videos. You could do push-ups on your knees.
I go to a gym with a wide range of ages. I don't know how old you are, but there are people at my gym in their eighties and nineties. Many of them are better at yoga than I am and can run further.