Here in the United States, many people prefer to use the word "custodian." If you are a custodian at a school, for example, a "good" custodian works hard to keep the classrooms clean: she or he carefully sweeps the floor each day, empties the wastebasket each day, and looks for any problems (e.g., burned-out lights). Also, when a good custodian cleans the restrooms (toilets), she or he checks to see that there is enough toilet paper and paper towels to dry one's hands. Sadly, some custodians are not "good." They are lazy. They just do a little work but not a really good job. They want the money but not the work. I do not know where you work, but if you have good custodians, you are very lucky. A good custodian is a great asset to an organization. She or he deserves recognition once a year -- a box of candy, a cash gift, etc.

This is a difficult question to answer because it will vary from job to job. A janitor is responsible for making sure that a building is kept secure and in good repair. Whether they do the work themselves or whether they are responsible for organising others to do the work depends on the size of the building and which organisation the janitor works for.