There are thousands of different tomato varieties, but all tomato plants fall into one of two categories: Determinate or Indeterminate. The first step to growing tomatoes is knowing which kind of plant you have.
Determinate tomato plants are predetermined to grow to a specific size and set a specific number of fruit. All the fruit on a determinate plant ripens at about the same time, and then the tomato plant is done.
Determinate tomato plants are smaller and bushier, and they do not need pruning. The only pruning that should ever be done on determinate plants is to pinch off the side shoots (suckers) that form below the first flower cluster. It actually does not make sense to prune any more branches off of these plants because they only have a set amount of tomatoes that they will produce and by taking off some of the branches you will be diminishing your harvest.
These tomato varieties are well suited to container planting and do not usually require trellising.
On the other hand, Indeterminate tomatoes will just keep on growing for as long as conditions are good. As long as you keep them happy, they will keep on producing more and more tomatoes. So rather than all the fruit ripening at once as the determinate plans do, this variety will give you tomatoes all season long.
Indeterminate plants are vining so they will get quite tall and will require support. A tomato cage is not really the best way to trellis an indeterminate tomato because the plant will only get as tall as you allow it to be, and an indeterminate plant can grow 10 feet tall or more if it has the support.