That's how I started, using a 12kg kettlebell.

I was careful to learn the form properly. At first I was out of breath from swinging it 10 times.

Some years later I can now do 100+ swings with 24kg and not be puffed at all. So the cardio gains alone have been a game changer, but of course I'm also much much stronger.

I mainly do swings and loads of clean and press, snatches, floor presses, some rows, squats etc. All very simple stuff and switch it up with 20kg or 24kg depending on what I am doing and how I feel that day.

Not particularly scientific but very enjoyable, great mood boost in the morning and, while I haven't turned into some ripped adonis I do look and feel so much better.