The rules used for naming alkenes under IUPAC system are similar to alkanes with some special ones.
i)The suffix to be used is -ene.
ii)The longest continuous chain should include both the carbon atoms of the double bond.
iii) The chain is to be numbered from the end that gives the lower number to the first carbon atom of the double bond.
iv) If there are two or more double bonds, the suffix used is -adiene or -atriene.
Some more examples