You have not provided enough information to provide a meaningul response, but in general:
(1) The "spine" is not usually "narrowed", however the small pasageways through which nerve pass betrween the veterbra may be come narrowed. This is often called spinal stenosis. Generally this is due to a damaged "disc" separating the vertebra. This compresses nerves, causing swelling, inflammation, and sometimes tingling, sometimes numbess, and other times pain and rerstrictions on range of motion.
(2) This is often due to a disintegration or swelling of the cartiliginous discs separating the vertebra. Surgery may take many forms. The most common type is the "laminectomy", in which a segment of the bulging disc is removed in order to reduce compression on a nerve (usually but not always the sciatic nerve when the problem is in the lumbar vertebra L1-L5). Cervical pain is another issue. Discuss with your surgeon exactly what procedure he/she is contemplating.
The procedure has a good record, but does not always relieve pain. The best sucess is from a surgeon who does a lot of procedures. Usually hospitalization is brief.