What is Alkane, alkyl group?

An alkane is a compound of carbon and hydrogen whose skeleton is a chain (linear or branched, not a ring) with only single bonds; its molecular formula is $\ce{C_{n}H_{2n+2}}$. An alkyl group is what remains of an alkane when one hydrogen atom is removed, so that it can be attached to a chain: methyl $\ce{-CH3}$, ethyl $\ce{-CH2-CH3}$.