Character Sheets: You can find them under the Journal tab in the upper right-hand corner of the browser window. Don't worry too much about why things don't look quite right, there is no magic world character sheet in Roll20, so I pulled a RuneQuest sheet. You can disregard most things, but you should be able to make skill rolls, weapon rolls, and characteristic rolls from the sheet as normal. Just keep track of lost hit points and magic points on your token (e.g. just enter +/-X in the red bubble and it will go up or down as required, the green bubble is for MP). If you need to make an armor roll just do it manually by entering it in the chat box. The syntax for dice rolling is pretty simple, it's just /roll [die +/- modifier] (replace the stuff in brackets with 1d8+1, 1d4-1, etc.)
NPCs that you control have all of their stats listed on the NPC sheet; this can be accessed by clicking the little gearbox icon right under the basic tab of the character sheet. Sometimes it reverts to the quick-start or full sheet, so you may have to open this up and select the correct tic-box to see their stats. There's only the most rudimentary stuff in there like their dodge roll and weapon skills and other basic characteristics, but you should be able to make dice rolls from it, when in doubt you can just roll manually.
Basic user interface tips and movement: There is a ruler you can access on the left hand of the map, or if you pick up a token and press the right mouse button it will start measuring the distance you have moved from your last position. To suspend snapping to the grid, press and hold the alt key before you pick up a token, then move it and drop it, they are just there to help with making quick measurements. In combat you can move 24 meters, out of combat you can move 72 meters per round. As long as you move your characters around inside the tree line you don't have to make any hide or move quietly rolls; the enemy seems fairly pre-occupied with the ritual that is taking place with the weird abomination of stitched together corpses near the base of the tower.
Llywelyn ap Gruffydd I gave you control of Solon (and you'll need to enter the stats for your summoned demon on the appropriate tab for Amon)
Siveon I gave you control of Mab
Grimgravy I gave you control of Urash, Bran, and Oona
As far as I can tell everything is good to go; HPs and MPs should be accurate for all of your characters. The basic combat order is posted below. If you want to make a move describe it in the chat box and move your token up to your maximum allowed. Since we're not in combat yet you can maneuver in the trees as you wish or make move quietly rolls and move up if you want. Once combat starts I'll call out your turn in the roll20 chatbox and you can make your move at your liesure.
If you have any issues, click on the help icon on the left hand side of the screen and it should give you all of the keyboard shortcuts and explain things better than I can.