FRESHMusicPlayer's main window can be divided into 3 parts.

The Navbar

The Navbar lets you navigate FMP and open auxiliary panes.

The left side shows tabs; Click to switch views.

The right side shows auxiliary panes; Click to open them. Click again to close. From left to right:

Keyboard Navigation lets you navigate FMP without using your mouse.

Content Area

The content area shows your currently selected view.

The controls box is where you control the currently playing track.

1 - Information about the currently playing track

Click the cover art or title to show more info about the track.

Right click the cover art or title to open the Overflow Menu, which lets you add the track to add the track to a playlist, open it in the tag editor, view lyrics, navigate to its entry in the library, switch to the Mini Player, and pause after the current track.
2 - Seekbar

Drag or click on the seekbar to seek. Click the indicator on the right of the seekbar to toggle between showing total time and time remaining.
3 - Previous

If you're at the beginning of a track, click this to go back to the previous track. Otherwise, this will seek back to the beginning of the track.
4 - Repeat

Click this to toggle between repeating the queue, repeating the current track, and not repeating.
5 - Pause/Play

Click to pause or play the track. (You can also press space to control this)
6 - Shuffle

Click to toggle shuffling.
7 - Next

Click to skip to the next track.
8 - Volume

Move your mouse near the volume icon to reveal the slider, then drag it to your desired volume. (If your cursor is not currently over a list, you can also use the scroll wheel to change the volume.)

If you're on Windows 10 or later and have System Transport Controls enabled, you can also use the media keys on your keyboard to control FMP.