A general example in Methane:
Where the firm lines resemble what lies on the 2D plane.
The dotted line resembles what lies backwards.
The Wedge resembles what lies forwards.
Making Methane actually look like this:
We use these denotations because molecules in real life are actually 3 Dimensional.
n.b. Lone pairs are very important in atoms in molecules because they define what else the atom can bond with.