If you're deskbound or otherwise sedentary consider one of those underdesk bike things. You're not going to be building any muscle or working your heart, but you'll keep your blood moving and prevent it from clotting (I've personally had this happen; it sucks, it hurts, and it leaves terrible scars).
If you're looking to just do some basic strength stuff then invest in some plates, dumbbells, and maybe even a curling bar. Keep an eye out for thrift stores. There are tons of simple routines you can run with just plates alone that get your chest, back, and arms engaged, and you don't need to go crazy. If you're just starting out then all you're going to need are a 25/35/45 (for a curling bar keep an eye out for pairs of lower weights, like 2.5's, 5's, and 10's).
The routine I like to run involves a few really basic plate workouts I was taught (I don't actually know the names of any of these)
1. Assuming a position similar to a squat (it's not quite, but you get your ass out in a similar way), let the plate rest with your arms hanging down. Lift the plate up into your chest.
2. Stand up straight, hold the plate in front of your chest with your elbows out. Push the plate outward, then bring it back in, and repeat.
3. Stand up straight, hold the plate above your head. Lift it, then bring it back down.
4. Stand up straight, hold the plate above your head like before, and work the plate around your back in a circular motion. If you're doing this right you'll be engaging your traps for this one.
In general, you can approach these by doing many reps with lighter weights, or you can try to do less reps with heavier weights. I tend to like to do a little of both, ending with the heavier stuff. Usually by that point I can't really get a lot of reps in, but what you can do are keep your muscles engaged for longer by doing the exercises in slow motion. For instance, when you bring the plate above your head, bring it down as slowly as you possibly can. Trust me, you'll feel your muscles working to do it.
I guess some other advice would be to not hurt yourself and be consistent. If you're just starting out, try to find the same time of day and just do a couple reps of something really basic and light. Don't worry about getting an actual workout in by going all in right away. Just build good habits first by consistently stepping up to do it, and when that becomes easy you can give yourself a harder workout. There was a kiwi here somewhere on some thread a while back that had said something like "find some time to do one single pushup every day, because it's impossible to mentally wrestle yourself out of finding the time for that". Once you're in that space consistently is when you stop feeling like it's a chore.
If any kiwis know the actual names of the exercises I described I'd appreciate it. These were just the things I was taught by a friend. I'll add that my first month of doing it would leave my arms unable to be completely straightened out, as I hadn't ever done serious workouts in my life. It's a really good feeling for some people that kind of soreness (I like it myself). If it's new to you, you might be all "what the fuck" but it's normal.