Before starting the most important thing before you will light the stove, is fill your Hot Tub with water for at least 90%. It seems so logical, but not following up this rule may seriously damage your heater or Hot Tub.
The Tub can be simplly filled with a garden hose. This will normally take about 1,5 to 2 hours with a standard gardenhose.
At the backside of your Hot Tub neart the inside heater you will find a waterdrain installed on bottomlevel with a hoseconnector on the outside. You may connect a gardenhose to the waterdrain to empty your bath.