I want to make a flat piece of brass with a ring soldered to it so it
can fit onto a keyring. I am lousy at soldering. Can anyone tell me exactly

Since your piece of brass is about .1 thick, I suggest drilling two
small holes in the edge. Make a loop from some wire of your choice
and stick the ends in the two holes. Solder with any kind of soft
solder. File off the excess solder and you will barely notice the
silver colored solder.

chuck