First you need a very large pot and a place that gets at least 6-8 hours of sun.
Make holes in the pot, if they are not there already. Put pieces of broken clay pots, rocks or broken bricks over the holes on the inside of the pot.
Fill with good potting soil that will drain well. I add hydrated soil polymers to retain moisture.
Plant the tomato plants. Patio type tomatoes are best because they won't grow so tall and viney. You may have to stake the patio tomatoes and will definitely need a stake for indeterminate kinds. Use bamboo, a 1 x 2 or buy a tomato cage.
Keep the plants well watered and fertilize after they begin to flower.