It is easy to close the Project Browser and Properties Palette, just click the little X in the top right corner of each window.
It is a little less obvious how to restore them. The formal Front Door is via the View ribbon tab > Windows panel > User Interface.
A bit less obvious is the access to Browsers via the right-click context menu, for the Project Browser at least.
I'm sure you noticed that the Properties Palette can be restored via the right-click context menu too.
It is also available on the Modify ribbon tab > Properties panel > Properties.
The Properties Palette also has two keyboard shortcuts: PP and CTRL+1, at least that's true of my configuration (stock install). There isn't one assigned to the Project Browser but we could opt to do that too.
Oh, Revit MEP users can close and open their System Browser with F9 as well as access it in the same way the Project Browser can be (described above).