Cyclobutadiene (more strictly cyclobuta-1,3-diene)
is 4 carbons in a cyclic (I hesitate to use ring more like square !) configuration with double bonds between two sets of carbon atoms.
or two ethene molecules linked by single bonds between the two carbons.
words are useless, piccies are better:
C=C
| |
C=C
the other valences in the carbon are of course hydrogen.
benzene is similar, but 6 carbons in a ring with three double bonds every other bond.
I'm not gonna try that one in Ascii art !!