Movement is about LIFESTYLE. Therefore think of it as something part of your daily activities, that comes as naturally as brushing your teeth or washing...life would be very uncomfortable without it...
If you move very little (i.e. you get up, get in the car, sit at you desk, back in the car and hop on the couch) you need to start with the basic: walking. You can even go wild and think about biking.
Thing is to find the small opportunities where you can use your beautiful two feet instead of this wonderful technology that is making us sick. For example take the metro instead of the car. Or the bus. Might take longer and be crowded but I am sure you can arrange to read a good book or find a time slot with less people.
Next step would be getting out a station before and walk. Or do a mix bike-metro(bus).
Also think about taking the stairs. Sometimes they look nasty and hidden, this is ok, we need to find something else. But at least when you take the metro don't push yourself with the crowd on the escalator. Take the stairs. There is nobody there. Enjoy the space and the movement. Instead of staying inert for 1min and absorbing useless advertisements or the sweat smell of people too close to you, do something better.
You might get panicked about all the time you will 'waste' walking. It is normal because we live in such a speedy time, but it is not ok. While walking you can ignore your phone. Take a break. Breathe. Focus on your body, breath, meditate. Look for quiet paths. You can listen to a podcast or an audiobook. You can call a friend or a colleague. But you will still be walking.
Next thing will be taking up an activity. I can already feel your discouragement. But it's normal. You want to find something that you really enjoy. With people you like. In an environment you feel GOOD. For this you need some time to try different things. Make sure it is easy to reach and it fits your schedule. You can use the new subscription models (like Gymlib ) which allow to try different gyms and clubs until you find a place you feel good. Same goes for dance classes or other sports.
Have patience and look for a coach and group that you really enjoy. 'Drag' a friend along.
Make sure it becomes a routine. A 'date' with your inner joy.
If you want to train by yourself and be flexible you can choose a personal trainer. They cost more but see it as an investment. Ask friends around, sure someone can recommend you a good coach. He can make you a training plan, explain the exercises and let you train a few sessions by yourself. He will get you started and motivated and you can see him only from time to time to reboost your motivation and update your training plan.
There are many activities, besides sports that can do you a lot of good: dance, hiking, biking, pilates, yoga, TaiChi, swimming, strechning, etc. You can do them outside in a park, in a small club or in a gym, at your or friend's place.
On a more general basis, think that life is movement. Life never stands still, so when you just sit and stare at your screen you are cut from it. You are cut from your body. Movement is being present to life.
It is hard to start moving, even for the most motivated athletes. Because we like comfort.
So take some time to move and pay attention how you feel afterwards, how your body is reacting to it. Only AFTER take a decision about moving.
Try for example to do a day where you move more and notice how you feel, how the flow of thoughts has changed and how you sleep that night.
Think also which priority you give to movement. What makes you not prioritize it more? Understanding what stops you so that you can remove barriers. Don't try it to do it by yourself. Ask for help and motivation. And once you get your body moving on a daily basis it will feel so good you will not want to stop.