Sketch’s interface is minimal by design.
The toolbar on the top contains the most important actions. The inspector on the right lets you adjust the properties of the selected layer(s). The pane on your left lists all the layers and artboards in your document, and your working canvas is in the middle.
There are no floating panels. Instead, the inspector will adapt to show you the tools you need at every moment, and hide everything else. That way you always have a completely unobscured view of your canvas.