Personally I find delfship is more trouble than its worth. Even though anyone can make a hull in it, it takes someone who is trained to make a hull that looks right.
But the basic Idea is that you make a new hull (click the "new" button) then enter the length and depth, along with how many points you want in the hull (general rule is for every 5 metres have 1 dot). Then simply drag the little dot things around until you get a hull that you like.
To be honest though, the best thing to do is simply play around with it, until you get to grips with the software
Don't be afraid if you don't get how it works at first, i've got a pile of 50 hulls on my PC, all of them failures!