Rob the part about the biscuit cutter might not be clear to you either. If you have a biscuit cutter, cut a piece of a spare stair tread that's as long as the width of the tread you will be using. Turn this so the grain of this piece runs perpendicular to the tread grain direction and matches the end dimensions. Mark for biscuit slots and cut them, being careful to cut the slots for the right side up if you do double biscuit. Glue the tread and end cap with the 4 biscuits and clamp them. Then rout the bullnose on the one long edge starting with the cross grain cut so you do not get tearout. Finally, sand and finish before installation. When you install, you can do a step at a time, if you wish and not disrupt the family for a long period. Drill and nail with most hardwoods.
There are a lot of ways to prep the treads for spindles to support the bannister and doing that part of it. I suggest that you hire a stair pro to do that part of it if you will be installing spindles, newel posts and so on. He should be involved before you install the treads.