Molecular formula for 4-methyl-1-pentanol? According to Wikipedia 4-methyl-1-pentanol is $\ce{C_6H_{14}O}$.

But here is what I got, which is slightly different.

Methyl = Think of methyl group, which is $\ce{CH_3}$.

Pentanol = Penta means we have 5 carbons, -ane ending means we have $2n+2$ hydrogens, i.e. 12 hydrogens and -ol ending means we have a hydroxyl group $\ce{-OH}$.

So the molecular formula that I arrived at is: $\ce{CH_3C_5H_{12}O}$ = $\ce{C_6H_{15}O}$. 

How did I end up with an extra hydrogen compared to Wikipedia answer?
Actually, the formula you arrived at is $\ce{CH3C5H12OH}$ = $\ce{C6H16O}$.  In any case, in your "2n+2" step, you need to reduce that number of hydrogens by 2.  One is eliminated where the methyl group is attached, and a second is eliminated where the $\ce{-OH}$ group is attached.  So removing 2 hydrogens from $\ce{C6H16O}$, gives you the desired $\ce{C6H14O}$.