Board houses take gerber files, NOT (Eagle) .sch and .brd files.
OSHPark is trying to make it easier for hobbyists by accepting gerbers AND Eagle files.
Gerbers are a set of files that simply tell the board house what each layer looks like. Top copper, top solder, top overlay (silkscreen), etc. For this design, there are 7 gerber files; they are all zipped.
Simply send that .zip file to the board house of your choosing. they will take it from there.
there are a bunch of options that each board house will have, but generally you will want
pcb thickness: 1.6mm (0.061")
finish: HASL (or ENIG)
copper thickness: 1oz
all other options are personal (colors, e-testing, quantity)
NC, USA