First follow the install instructions on this website:
Now launch OCTGN
Go to PLAY tab and click START
Accept the default password and such (or change it if you want to. Once you start a single player game no one can join anyway).
Click START again in the lobby
Load the QUEST deck you want to play (in this example Passage through Mirkwood)
The cards will automatically be loaded and the setup will be done automatically. Decks are located where you installed OCTGN.
Now load your player deck. Either one you created or a default core set deck such as shown below:
The game is launched and you are ready to start ROUND ONE. Your initial hand of 6 cards is drawn for you. Remember you can RIGHT CLICK and take ONE mulligan if you want.
PLEASE NOTE: Player cards are listed on the player tab and the ENCOUNTER deck is listed in the GLOBAL tab.
Encounter Deck Tab (click GLOBAL):