Methane is a good example of four single
covalent bonds.  Notice that the hydrogen
electrons (in red) are being shared with the
Carbon atom.  

Shown below are two more ways to show
the same formula. One using
electron dot
and the other using a line bond
Here you can see how
electron dot diagrams
and line bond
diagrams can
represent double and
even triple bonds.
More Covalent Bonds
Here is a short video on
covalent bonds.  It's works
best with a broadband