difference between hexane and hexane fraction
The difference is simple. Hexane, if that is what the label says it is, should mostly be n-hexane. But hexane fraction is any hydrocarbon that distills at close to the same temperature as n-hexane. This mostly means a mixture of other six-carbon hydrocarbons (e.g. 2-methylpentane) most of which boil between 55 and 70 °C. You might find that the mixture contains some C-7 hydrocarbons as well.

For many reactions what you need is some volatile hydrocarbon and it isn't that important that it is a mixture. Occasionally, though, this will affect a crystallisation (especially if the hydrocarbon is bound in the crystal lattice). Pure hexane will work better in that case.

The reason why they are sold as different things is that pure hexane is a lot more expensive to produce as it will require careful distillation to separate it from the other, similar boiling point, hydrocarbons. So you don't want to use it if the cheaper mixture works. The cheaper mixture will just be a fraction obtained from crudely distilling petroleum at around 60–70 °C.