Once the must has cooled, it can be transferred to the primary fermentation chamber. Waiting until the must is room temperature is especially important when using glass jugs or carboys. The thermal shock from adding a hot liquid to a cold glass container (or vice versa) can cause the glass to crack or shatter.
Before you pitch the yeast, add any remaining ingredients or adjuncts that your recipe calls for. If the must has not been aerated previously thru pouring, vigorous stirring, or shaking it should be done now. Dry yeast should be activated to verify that it is viable and healthy before pitching it into the mead. If using liquid yeast, follow the manufacturer’s instructions. Once the yeast has been pitched, mix the must and take gravity readings if you desire to determine the starting gravity.
Seal the primary fermentation chamber with a fermentation lock or blow-off tube. The fermentation chamber should be moved to 
a dark space where it will not be frequently disturbed. Within 24 hours you should notice bubbles rising and the airlock will be burping periodically. This indicates that the yeast are active and are metabolizing the sugars in the honey.
As long as the yeast has access to oxygen it will reproduce. This is important because we want a healthy yeast colony that will crowd out competing microorganisms. Once the oxygen has been consumed, the yeast stop reproducing and begins producing alcohol. Under normal circumstances, the yeast will continue to produce alcohol until all sugar has been metabolized out of the must or until the alcohol level becomes greater than the yeast can tolerate.
Primary fermentation can take a few days or a few weeks depending upon many factors. The amount of honey, temperature of the must, pH, nutrient level, and yeast strain are just a few of the factors that influence how long the primary fermentation lasts. Once the fermentation lock stops bubbling regularly it is time to rack.