Let me simplify as far as possible.
There vertebrae in our vertebral
column and each of them is numbered
In between each of these vertebrae there is a disc which is meant for lubrication and mobility
Some times the disc slips from its regular position and then it can compress on the nerve
roots which Exit from the opening between two vertebrae. This is called enchrochment. Disc bulge means that there is mild backward protrusion of the disc
Hope I have simplified enough to meet your satisfaction