Spaceships 3, tactical combat, calculating ralative velocitie instruction help

[Jaware]

As the title put.

I am having immense trouble decifiing the paragraph on page 31 instructing how to calculate relative velocity when you're in different possistions.

That paragraph is very..... Hard... to decipher and the example doesnt help at all.

Can anyone provide me with the help that i need to use this system?