First, you want to identify the largest number of sequential carbons. In this case, the parent chain is made up of 4 carbons. This makes the base name, butane.
Next, you want to identify any branches. There is a branch made up of 1 carbon, and these are referred to as a methyl group. The lowest possible carbon on the parent chain this branch is attached to is the second carbon.
When you put these factors together, you are left with the name: 2-methylbutane.
