The answers to many of your questions depend on the actual procedure you are having done. You may or may not be on crutches. You may start physical therapy immediately, but you may have a delay. Depending on your job (desk job? on your feet a lot? construction work?) you may only be out a couple of days, but it may be much longer. Actually that depends on your job and the procedure combined.
As to swimming - generally you can submerge the knee in water after 2-3 days from an arthroscopic procedure. But how long before you can actually swim goes back to all the other unknowns.
If you know the name of your procedure, you can probably get some very detailed responses on this board. Either way, good luck.