When is a good time to start strength training?

solpwr

It's a great thing to do, but don't sweat that you are just getting started. This is a lifestyle, when you've been doing it for 20 years, you'll look back and the few months at the beginning will be inconsequential.
I have been lifting on and off for more than 30 years. I have found that I take off lifting from May-September when I drop my gym membership and focus on cycling, mountain climbing, and the like.
That said I tend to be muscular, so I don't lose much.
But you asked what you should do: Think of major muscle groups. Core, chest, shoulders, back, arms (biceps/triceps), quads, glutes/hams, and calves. Start with 2 sets x 12 reps for each of those body parts 3 times per week. So that's 18 sets right there to start.
You will find that you will have to add, go to 3 sets of each movement. Then find another exercise for each body part, and go back to 2 set times 2 exercises. In a month, you should be lifting enough weight that you can only do 10 reps of each movement.
A way to speed things up if time is at a premium for you is to super-set. Think opposite muscle groups. Do a set of bicep curls followed by a set of tricep pushdowns without a rest, then go back to biceps. This can be a good way to start out. Chest and back, biceps and triceps, glutes/hams and quads, core and shoulders.
Find a movement for each major group. Don't neglect your legs. Guys especially like to work out upper body only and end up with spindly little legs. The leg muscles are the largest muscles in your body.