Side shoots should be removed from tall varieties that are also called indeterminate or Cordon.
This keeps all of the new growth in the main stem from which the leaf branches and eventually the trusses grow.
Here you see two side shoots growing between the main stem and the leaf branches. You can remove these side shoots when they are about an inch or two long.
Trusses eventually grow from the main stem. They look like leaf branches to begin with, but then grow flowers on the end of the branches.
The flowers eventually fade and small pea-like tomatoes are formed.
If you are growing outside in a short season area, you would expect to grow about four trusses of tomatoes before stopping the plant by pinching out the growing tip.
For more information please visit: http://www.tomatogrowing.co.uk/html/side_shoots___trusses.html