The short version:

1. Select your advertised maximum speed from the "connection speed" slider bar. (the maximum available bandwidth, in kilobits per second).
2. Choose your Network Adapter, or check to "Modify All Network Adapters".
3. Choose the "Optimal settings" radio-button near the bottom of the program.
4. Click "Apply changes", and reboot when prompted by the program.

The right version: Find your Maximum MTU value, learn what all the settings mean, and tweak them accordingly using The Optimizer in custom mode :)

Note: With version 2 of the TCP Optimizer, we've also included full online documentation.