Alkyl groups:

Alkyl groups that are represented as C_nH_2n+1 are alkane substituents of a complex molecule. Simple alkyl groups can be pointed out in skeletal form, or like CH₃, CH₂CH₃, CH₂CH₂CH₃, et cetera.

Figure:  Drawings of an alkyl substituted cyclohexane.

Note:  how the CH₃ groups have been written in Diagram. The structure in Figure (a) is more correct as compared to the structure in Figure (b) because the bond displayed is between the carbons.

Figure: (a) Correct depiction of methyl group; (b) wrong depiction of methyl group.