This is the "flow" where players, monsters, traps and notes live. You can drag and drop them to re-order them. By default, you will see only a name and some other info (such as hp and initiative modifier) but clicking a checkbox will cause more information to appear.
This is how you create things that go in the flow. You can create monsters with either all book information (all info) or just name, hp and initiative modifier (min info). NPCs and traps require all info, and notes can be as long or short as you'd like.
This is the "stack" where you keep track of initiative. Drag monsters, players, etc from the flow into this area. You can only add one instance of each player, but you can drag multiple instances of monsters, traps, etc. Drag-n-drop them elsewhere to remove them. When a person or monsters's turn is over, click the down-arrow to send something to the bottom of the stack. You can always click on and change the listed hp, initiative. You can use the  areas to keep notes, like how long a participant has a certain status effect.
These buttons add participants from the flow to the initiative stack.
These buttons remove participants from the initiative stack.
You can use these for easy initative sorting. "Roll initiative" will randomly roll a d20 for each monster/NPC and add their initiative bonus. (You will have to type in the players' initiatives when they roll them.) "Sort by initiative" puts everyone in order, and "Number Duplicates" will assign unique numbers to any duplicates you've added to the stack.
Click this button to hide most info. Click it again to restore the info. Useful if you have to show this screen to the players. No spoilers! (Note that player names and info revealed by checkbox stays revealed, though.)
Finally, these buttons provide ways to save your flow. Browser storage is similar to cookies, and can be lost if your browser screws up or you delete cookies/storage. To make doubly sure, use the Export button to save a copy of your flow elsewhere.
Don't forget to check if the bugbears next door hear any of this!
Type: mechanical; Perception DC 20; Disable Device DC 20
Trigger: location; Reset: manual
Effect: Fall 20ft, 2d6 damage. Reflex save DC 20 to avoid.
CE small humanoid (goblin); Senses: darkvision 60ft; perception +1