A cordless screwdriver is a power tool designed to insert and remove screws and drill small pilot holes (a hole drilled prior to inserting a screw).
Cordless screwdrivers are generally smaller, lighter and less expensive than cordless drill drivers.
However…
Cordless screwdrivers are not very powerful and are designed mainly for driving smaller screws in softer materials (e.g. softwoods).
If you want to drill large and small holes in a variety of materials as well as insert or remove screws, then it’s recommended that you use a cordless drill driver.