Indeterminate/cordon tomatoes are pruned so that you have 1 stem that is pruned so I can be trained up a string/cane, because the stem carries on growing upwards and producing more tomato trusses as it does - they can give a huge yield for the space they are growing in.
Bear in mind if you don't prune the side shoots off you will have an uncontrollable/unsupportable mass of stems
Once you know what you are doing, it is possible with good feeding and watering to have 2 main stems per plant (a double cordon)- but that's for another post
Determinate tomatoes grow a few stems from low down (like a bush) and produce a flowers/fruit at the top of each stem, and then the stem stops growing. They are like the average small, basket varieties - just a good bit sturdier. These need more canes around them for support to stop them falling over with the weight of tomatoes..
Most determinate varieties produce all their fruit at around the same time, so a much shorter period of harvest compared with the cordons. This is good if you want to make a big batch of pasta sauce, but not so good if you want to eat salads all summer
To add to the confusion there are some tomatoes that can't make up their mind called 'semi determinate' and they do their own thing and need an awful lot of support and tying in IMO