Cerebral Spinal Fluid (CSF) is mostly made in the ventricular system of the brain. This fluid then circulates throughout the brain as well as down the spine. This is the same fluid which is obtained with a spinal tap (lumbar puncture). Place your mouse arrow on the picture and click the forward arrow. Notice how the fluid filled structure (drawn in purple) occupies space in all the lobes of the brain.

This picture shows how the csf flows within the ventricular system. When it reaches the end it circulates down into the spinal cord and out into the brain. When there is too much fluid in the ventricular system, it dilates and can squeeze the surrounding brain tissue. This is hydrocephalus.