A 'normal' staicase consists of 2 stringers (the outside edges of the stairs), treads (to put your feet on) and risers (the vertical bits between the treads which may be omitted if you want open plan). A staircase may only have 13 treads until there must be an intermediate landing. The vast majority of stairs used on modern building sites are prefabricated, which of course saves a lot of time, but is more expensive. If you really want to do it yourself, it is fairly straightforward if you are a decent carpenter, otherwise nip down your local builders merchant and see what they can do. If you get a prefabbed one all you have to do is fix it top and bottom.

One step at a time?