When you plant in containers -- whether growing indoors or outdoors -- you mustn't use actual dirt. It doesn't drain well enough for containers. Also, there can be bad microorganisms, molds, bugs or their eggs, and weed seeds.

At the garden center or big-box store, look for bags labeled "potting mix" or something similar. If anything says "potting soil," check the ingredients carefully to make sure it doesn't contain any actual dirt.

In the Growing in Containers forum, they argue the fine points of container mixes. Al's 5-1-1 is 5 parts bark fines, 1 part peat moss, and 1 part perlite, IIRC.

Those who grow tomatoes in containers do re-use the used mix to some extent. You may find a thread where they discuss what to discard and what to keep; then they add some new mix to the old stuff and plant. (Whatever container mix you discard can be added to the compost or garden beds.)