The Selection Home allows you to roll attacks and damage for monsters. The order of the monsters is the same as the D&D 5e Monster Manual (missing a few as it is the SRD list), or almost exactly the same as this website here: https://open5e.com/monsters/index.html .
Once you have selected all the attacks you would like to do as well as the 'use monster' button found in each monster's menu if you are using at least one monster of that kind. As well as the 'Send Monster x to Battle' if you are using monster x in that Monster's menu, press the green 'Send Creature/s to Battle!' button at the bottom of the screen.
This should take you to the results page.
The results should turn up if they don't the most common reason is that eg. for a Balor, the 'Use Balor' button on the previous page has not been selected.
The biggest difference is that the advanced selection rolls for advantage/disadvantage.
It does this by rolling a second attack roll for each attack selected (as well as sometimes having to re-roll damage, eg. if you get a critical hit on the second roll and have advantage). The reason why I have not just replaced the main roller with this is because it could be quite confusing for new users.