Basic navigation and settings are easy: go back and forth with the right and left arrow keys, and hit the Escape key to close. The little boxes with MM in them means that function is muted, or disabled. Toggle the M key to mute/unmute. 00 means zero volume, so use the up and down arrow keys to adjust it. When there are two channels you can adjust each one independently, which you can see in the Master setting in Figure 1. Q increases the left channel, and Z decreases. E and C control the right channel. In the Capture screen, use the spacebar to select the active recording device.
Most of the settings are self-explanatory, but there is oft confusion over Master and PCM. Master controls your playback volume. A PCM device is like a virtual soundcard; this is the bit that converts analog sound to digital. It can be either software or hardware. Your Linux sound applications need the PCM channel. So you usually need both of these active to enable playback.