Let's say, for the sake of example, that you are framing a straight line staircase of one complete story. Let's also say, for example, that the entire distance from subfloor of floor 1 to the subfloor of floor 2 is 108 inches. Lastly, let's assume that no matter how "long" this staircase is, you aren't going to run into anything like structural steel beam or a basement foundation wall or anything cute like that.
With this in mind, the generally accepted "average" stair has a 7" rise and an 11" tread. The tread is the part you step on, the rise is the part you stub your toe on. The absolute MUST here is that at a uniform distance from the handrail, (Usually somewhere near 16") EVERY stair must be identical in rise and tread, or else you have a trip hazard, which when we are talking about a full run of stairs, is BAD.
So, if we have 108" of vertical distance to span, we divide that number by 7 and come up with 15 with a remainder of 3". So, we could either have a staircase with 15 rises of 7 and 3/15" or we could have 16 rises of 6 3/4". Personally, if you have room for the extra length, go for 16.
So, at an 11" tread, you will have a stair case that has 15 treads, or a total of 165" long, or 13'9" long.
Now go to sears and by a framing square and two framing square clamps, which are hexagonally shaped brass nuggets with a slot cut in the side that fits over the square, and a screw machined into the side of the nugget that clamps down onto the square to hold it in position. You want to set your clamps up for an 11" tread and a 6 3/4" rise, then lay out your stringers with the square so that you end up making a jagged line all the way up. Make sure you lay out the top and bottom of your stringer so they sit square with the top floor header and the floor of the first floor.
I can't draw pictures here, so if you don't understand this part, it's time to buy a book from Ortho, Sunset, or Home Depot on basic framing.