When entering information what do the 'box' numbers refer to?

When entering information what do the 'box' numbers refer to?

To help make entering the data as easy as possible where possible we make reference to the box number on the tax return that will be updated. 

For example in the example below, taken from the Trust schedule (SA107) if you were to make an entry in the highlighted area then Box 1 on the SA107 would be populated.