General rules:

Numbering must begin from the end of the main or parent chain nearest the functional group. Hence, the numbering should position the alcohol at position 1 and not at the position 4.

Figure:   Numbering of the longest chain.

The position of the functional group has to be described in the name. Hence, the alcohol is a 1-butanol.

Another substituents are named and ordered in similar way as for alkanes. The alcohol comprises an ethyl group at position 2 and thus the full name for the structure is 2-ethyl-1-butanol.

There are another rules designed for particular situations. For instance, if the functional group is an equivalent distance from either end of the main or parent chain, the numbering begins from the end of the chain nearest to any substituents. For instance, the alcohol is 2-methyl-3-pentanol and not 4-methyl-3-pentanol.

Figure:    2-Methyl-3-pentanol.