Here is a small "Sungella" tomato plant, which is ready for planting-out. This would be a good time to remove the first of its side-shoots.
The side-shoots can be removed with a pair of secateurs, or if small then simply with finger- and thumb-nails. This next photo shows the bits that should be removed.
Here's the plant after surgery...
Side-shooting is not a one-off task. As the plant grows, you will need to repeat the operation at frequent intervals, and it is best done before the side-shoots get big. With the "determinate" type tomatoes, side-shooting is not normally practised. This sort of tomato is deliberately grown short and "bushy", and the side-shoots are seen as beneficial.