Alkyl is a group of chemicals with carbon atoms. They are like alkanes but they have one fewer hydrogen atom. An alkyl is a piece of a molecule that makes it do or act a certain way. Alkyls have only carbon and hydrogen atoms, in a chain.
Alkyl groups have this formula: C<subs>n</subs>H<subs>2n+1</subs>, where n can be any number so long as it is the same one. (For example, if there are two carbons, there must be four hydrogens because 2*2=4.)