If you add fruits and herbs to it, you will notice bubbling and foaming in the top portion of the bottle, within the first 12 to 24 hours of making it. This is normal, but it will need to be cleaned. Failing to do so will clog the airlock, leading to a possible explosion of the bottle.
Once six weeks are over, check the airlock again. It should ideally have stopped bubbling. In some cases, it could also slow down, if not completely stop. When the bubbling stops, it is time to bottle it.