Cyst is a term that in very simple words is a sac / cavity with a lining and containing fluid within. It may arise due to a multitude of reasons ranging from infection to injury or may even be developmental.
These cavities may arise within bone or soft tissue (skin / muscle) and may expand with time at the cost of adjacent structures.
The symptoms experienced by a patient may include :

Swelling

Pain

Tingling / numbness

Fluid discharge

Restricted mouth opening

Teeth becoming loose

Change in facial appearance
They need to be operated upon. The procedure may be minor or major entirely depending upon the size of the
cyst and the structures involved. It may be carried out under Local / General anesthesia.