OK, you want to be sure you know the condition of chimney flue and what you've got. You'll notice my response is all about the chimney more than the stove. That's where the heat and fuel goes when not right. The ideal is an insulated flue the same size as stove outlet on any stove or insert.
Keeping the flue above 250* f all the way to the top is the object to avoid condensing any moisture going up the flue. Below that temp, smoke particles stick and can form creosote rapidly. Correctly seasoned wood makes a big difference as well. In theory, keeping the inner flue hot enough all the way up without leaving excess heat up is the most efficient use of the fuel. With a stove having single wall pipe that you can check the temp where it dumps into the chimney flue, it's then a guess as to how much heat is lost by the chimney. An Insert in your case is difficult to judge, so you need to check for creosote often until you know how much you're creating. Indoor chimneys are best for keeping hot, and the flue size is critical for how much heat you need to leave up. Some fireplaces were built with very large flues and require much more heat to keep above the 250* threshold. A liner in the flue reduces the internal size and can be insulated to make even more efficient. So you need to know the size of flue all the way up to have an idea of how much heat to leave up. Your insert outlet should be about 50 square inches, or a 7 X 7 masonry flue. You can see when the flue measures larger, it can require twice as much heat. This is not just to prevent creosote, it is the basis of what makes the stove work. ALWAYS remember the basics;
The chimney is the engine that drives the stove. The rising gasses in the chimney cause a low pressure area in chimney and stove, and atmospheric air pressure pushes the air into the stove intakes to fill the void. This is the oxygen that makes the stove go. So it's more about the chimney than the stove. The lever on the right operates the damper which controls how much heat goes up, changing how much air comes in. A large or inefficient chimney will eat wood using most of the heat to keep the flue hot enough to work. (Damper open) The more efficient chimney flue (correct size) the more the damper can be closed. No one can tell you where to set it since all chimneys are different as well as outdoor temperature, elevation above sea level changing air pressure, and weather related low and high pressure areas. As temperature and air pressure changes, you will find minor adjustments are necessary much like keeping a steady speed with a vehicle up and down hill. With practice it becomes easier and you will get better efficiency.
Always open damper fully before opening door.
Once you get good and end up with a pile of coals in the morning, you'll find you can remove some fine burned ash from the front each day and rake the coal pile ahead to reload on. Cleaning ash with warm stove and damper open draws any fly ash into the stove preventing ash dust in the house. During times of burning coals down there is no smoke, so damper can be closed more to take advantage of this heat extending burn times. This burn cycle prevents the need of leaving fire burn out to clean ashes.
Always put ashes in METAL bucket for disposal. There will be glowing coals for many hours in the ash. Learn proper ash disposal !
Here's a thread with blowers shown.
https://www.hearth.com/talk/threads/made-a-blower-for-my-fisher-insert.117672/#post-1600025
You only have natural circulation to bring the heat out from around the back. Your Insert is double wall and instead of radiating like a single wall stove, you're heats the air with convection around the inner shell and the hot air only drifts out. The blower makes a huge difference removing the heat from the hottest part of the insert around the outlet vent area.
The manual has a cut away to show the air flow path on page 7.
Read the entire manual.
Read up on any threads about Inserts on this forum and you'll get a good idea of operation.