Ball Joints?

[90 accord]

what is the main function, and secondary, if there are any of a ball joint?

do all cars have an upper and a lower? whats the purpose for each?

 

[CRX-YEM]

not all cars have upper and lower ball joints.

Dual Wishbone Suspension has two ball joints
connect the spindle to the upper and lower control arms
they also allow for the spindle to rotate while sterring

A Mcpherson Strut type has one ball joint
a lower ball joint which connects to the spindle which allows the spindle to rotate while sterring.
the mcpherson strut assembly rotates and connects to the top of the spindle in a way it replaces the need for an upper ball joint.