One of the best things you can do as you begin your strength-training journey is to get a trainer. You'll have far fewer injuries and more efficient workouts if you do.
Most gyms have them. Here at my Y, membership includes three free sessions with a trainer of your choice. Lord knows they are worth their weight in gold. After all, you're in it for the long haul, so why not get accurate information on how often to lift, what weights to use, and how to do the exercises correctly?
This is especially true if you're older. When you were a teenager, you could bang out any exercises and be fine. Form didn't matter because you had a huge margin for error. But if you're going to have a successful Third Act in life, the right technique is absolutely critical. The cost of doing this wrong just isn't worth it.
Ask your gym what trainer they recommend for you. Find one who is sympathetic but who will also push you!