How do I transition between two floors that are the same height?

You'll use a t-molding for this transition. You will also need sand paper and a general construction adhesive.

Before using adhesive, test to see if the track from the t-molding can slide gently underneath the existing floor. If not, you'll need to trim one edge of the track to bring it closer to the existing floor.

Sand the bottom of the track, lay a strip of glue down, and install your track directly on top of it. Be sure to leave about a 1/4" gap between the edge of your flooring and the center of the track for expansion space.

Continue installing your floors on the other end until you reach the track. Again, make sure to leave a 1/4" gap. Then, all you have to do is snap the t-molding piece into the track.