Summarize the following:
Most pool tables are made to be adjustable, so you can make them level, regardless of what surface they're on. Some pool tables may have metal plates, which can be added or removed to raise or lower the sides. Other pool tables have adjustable legs, with feet that can be screwed clockwise or counterclockwise, to raise or lower that side. Your owner's manual will provide specific information about your pool table.  If you don't have the manual, just look at the legs to see how they're put together, and whether or not they have adjustable components. If your pool table does not, you can still use shims and other tiny adjustments to level the table. If the table features screw-in feet or legs, they'll usually be raised by turning them to the right and lowered by turning them to the left. But always defer to the owner manual to be sure. Sometimes, the bolts and screws used to assemble a pool table can loosen slightly over time, resulting in the table becoming off-level. If you tighten up all the attachment screws, you can sometimes level out the table without even adjusting the height. Pool tables involve any number of different screws and screwdrivers to tighten. Look at the screws themselves to figure out what you need, or consult the owner's manual. If your pool table is adjustable, raise the lowest corner of the pool table by one degree, the least it can be adjusted. Leave the carpenter's level on the pool table, and check for the change. If that was too much, and the table has been unleveled in the wrong direction, lower it back to where it was and use shims to make smaller adjustments. More on this in the next section. Sometimes, you'll have to make lots of little tweaks on different sides to get the top of the table completely level. It's partially a trial-and-error process, so don't get discouraged. Leave the level on the top of the table and check for level after every adjustment. You can also leave the over adjusted leg as it is, and use shims on the over levels, if you'd rather. It's partially a trial-and-error process. Shims are small, tapered shards of wood that you can use to fill gaps and adjust the height of things like pool tables. They're commonly sold in the carpentry sections of any hardware or home goods store, usually in packages with variable sizes. You can trim the shims to fit underneath the feet of the table if necessary, to make sure that they don't show. If the feet are big enough, though, you may not need to worry about it. Have one or more assistants lift the corner of the table that needs to be raised. Carefully, place a shim underneath the leg, lowering the foot onto it gently.  Use the carpenter's level to check the balance of the pool table. See how the shim has affected the level of the top. Continue to add shims underneath the legs until the pool table is balanced. Move to other corners if necessary, to make other adjustments. Pool tables don't need to be absolutely flat for them to work well enough to play on. If you can get it close enough, but not totally perfect, don't keep adding and removing the same shim over and over.  Roll a couple balls to see how true they move. If it looks good to you, go with it. Do the marble-and-glass test again. If it sits still, you've got a playable table.

Summary:
Consult your owner's manual, if you have it. Tighten all attachment screws under the table. Raise the lowest table leg one degree. Adjust the other table legs, if necessary. Use shims to fine-tune the level. Get a few helpers if you need to add shims. Quit while you're ahead.