Simply put a certain amount of the essential oil in alcohol and stir. The alcohol should be strong, at least 90%, and as odorless as possible.
Add as much as you like as long as it dissolves in the alcohol. An old fashioned perfume contained up to about 35% fragrance in 100% perfume, a splash cologne can contain as less as 1% fragrance. So to 100 gram alcohol you can add 1-50 gram essential oils, as long as they do dissolve. This is different for the different kinds of essential oils.
The best place to get alcohol depends on the country / state you live in.