Mixere contains a number of control bars, including Volume, Snapshot, Tempo, Mute/Solo Fade, Master Volume, and Crossfader. All of these control bars share a common set of properties:
When a control bar is docked, it's part of the main frame, or the document frame, depending on what kind of bar it is. Master Volume and Crossfader dock to the main frame; the others dock to the document frame, and are referred to as "document bars". When a control bar is floated, it becomes a separate window that sits on top of the document.
Control bars are docked by default. To float a control bar, left-click on the bar's background (anywhere that isn't a control, e.g. the bar's caption), and while holding down the left mouse button, drag the bar away from the frame. To dock the control bar, drag it back onto the frame. Control bars can also be docked or floated by double-clicking on their background. Note that Mixere only allows control bars to be docked to the top or bottom of the frame, not to the sides. Also note that document bars can only be docked to their own document.
If you're having problems docking, it's probably because you're trying to dock to the wrong frame, or because you're trying to dock to one of the sides of the frame, instead of the top or bottom.
Control bars can be horizontally resized, but only while they're floating. To resize a bar, first float it, and then position the cursor over the bar's left or right edge. The cursor changes into a double-headed horizontal arrow, indicating that the bar is resizeable. Left-click and drag to resize the bar. The bar will retain its new width when docked. Bar position, docked vs. floating, and width are all persistent, i.e. they're saved, either with the document, or in the registry. Note that bars can't be made narrower than their minimum width.
A control bar can be shown or hidden using the same shortcut key. For example, pressing V shows the Volume bar; pressing V again hides it. When a control bar is visible, a check appears next to its name in the View menu.