The handbrake provides some braking effect if the hydraulic system fails, but it is primarily a parking brake. It acts on the same brake drums or discs as the hydraulic system, but separately, and it must be adjusted separately. Some systems have a primary and a secondary cable. On this one the secondary cable operates the brakes through a yoke attached by a clevis pin to the primary cable.
There are many types of adjuster, but they all have the same effect that of shortening or lengthening the cable.