First up, no '1-ol' doesn't mean there is one OH, the 1 signifies the position of the OH group in your parent chain (here ,hexane) which in this case is the C1 carbon. How many OH groups are present is represented by adding di/tri... as a prefix to '-Ol'.
You need to learn how to identify and number a parent chain in organic compounds first in order to make the structures of orgo compounds using their IUPAC names .
Anyway, OH group will just attach to a terminal alkene of hexane and whichever terminal you choose, you need to number it 1. This will cover the hexan-1-ol part.
The carbon in your parent chain, adjacent to the carbon you just numbered , would be numbered 2 and so on and so forth until you have covered all the carbons of your parent chain.
Now just attach a methyl group on the carbon numbered 2 and another methyl to the carbon numbered 4 and that will cover your 2.4 dimethyl.