After surgery about 80% of fistulas will be permanently cured. a fifth will recur.
Typically, the excised fistula is left open to heal. During this time you will need a dressing. Keep the wound clean, by washing regularly (at least once/day with plenty of tap water; twice a day is even better).
You need a dressing mainly to prevent your clothes from getting soiled by the open wound.
It should heal in less than four weeks after the operation.