All one needs to cycle a tank is some dead organic matter..
Could be just some pinches of flake food.. Could be a simple table shrimp that you put in the water for a few days..
Could be a little bit of ammonia..
Could be a little bit of urine.. yep
You basically need to get something "decaying/breaking down" or replicating decaying (ammonia) and the bacteria magically comes and starts doing work..
It can be as simple as
Fill tank with sand/rock/saltwater.. Get all equipment up and running then for a few days/week or so put some pinches of flake fish food in there and wait..
This process can take a good 4 weeks or more..
During the process ammonia will start to rise.. Then nitrites as the bacteria is turning the ammonia into its lesser toxic forms.. Then nitrates..
Once ammonia and nitrites are down to zero then you do some water changes to get nitrate levels where you want and you are done with a cycle.
Now you can purchase all sorts of "bacteria in a bottle" products and all other sorts of "cycling" products.. NONE are needed.. But you can have a shorter cycle because of them.. aka dumping a bottle of bacteria into a tank speeds up the process of bacteria being established and growing to useful populations..