When the board file first opens it may look like a mess. There are numerous layers used for the board definition, things like the copper, holes (drills), silkscreen (labels), etc. You can selectively turn these on/off to clean up the view.
To bring up the Layers dialog, click the layers icon in the upper left corner of the board layout window.
To turn on/off an individual layer, left click with mouse button in the eyeball column. If the eyeball is shown, the layer is visible.
Multiple layers can be selected by dragging with left mouse button, using <CTRL>+left button, and/or <SHIFT>+left button.
Then use the Show Layers and Hide Layers buttons to turn on/off all selected layers.