There are two main types of insulation: roll and batt insulation and loose fill (sometimes known as blown-in).
Loose fill insulation is best for tight spaces, or if your attic already has a layer of insulation that needs topping off. Wood joists allow air to move through the spaces, so they must be covered with insulation. If you choose loose fill insulation, this will take a special machine to install it.
The type of material you use is up to you. The most important consideration is the insulation’s R-value, or resistance to heat flow. The higher the R-value, the more resistance. Your region or your climate will determine the necessary R-value. Typically, the colder the climate, the higher the R-value you’ll need.