The bike: Stock Schwinn Trailway.

The primary goal: Extract and service (replace) the bottom bracket, which is making a clunking or popping noise

The secondary goal: Expand my toolkit

Seems simple, but I am confused about a few details. The questions:

1) How on earth do I find out what size BB these bikes have? I found out that they're "Square Taper" types, but looking up replaces leads me to a prompt for sizes.

2) What specific tool would do the extraction? I know what it looks like, but I don't know which one is exactly right.

Thanks!

M.