Alkyl Groups

When a branch off the main chain is present a secondary prefix is needed to indicate the
identity of this substructure. A locant (a number used to indicate the position of
attachment of the substructure to the main chain) must be used.

e.g 2-methylpentane showing the methyl group in the 2 position.

The side chains (branches) are named by using the appropriate root name while
modifying the ending to "yl".  So in this case the group is derived from methane so it becomes methyl.

Ethyl Group

Don't forget there are many ways to represent groups in organic chemistry.  For example, we could draw or represent the ethyl group as follows.  The ethyl group is attached to a hypothetical R group.  Think of the R as a joker or wild card, it could be anything.

Here is ethyl benzene.  The R is a benzene ring.

The side chains (branches) are named by using the appropriate root name while
modifying the ending to "yl".