Although, if you want to create a gamebook, most people prefer using Squiffy to create those.
Also, welcome to the community!
I highly recommend planning your game on MSPublisher or a text document on PC, so you can easily duplicate copy/paste your text right into the Quest online editor. I say the "online" Quest editor, as I tried the "offline" one found it had too many confusing problems.
Your game will evolve as you get more ideas once you start, so it is best to have a well planned rough guide for yourself before you even begin on the Quest editor. It is fun doing the planning stage. Mke a map and start puting objects in your rooms. Keep it simple to start with and then add more stuff in once you have a good idea of what the objective of your game is.
Once your ideas start flowing, you will eventually decide on what objects will be and where you find them etc. Then you can list objects, rooms and characters (if any are in your game).
"Locations" or "rooms" can vary from being massive to tiny e.g. You are in a lagoon. You are inside a matchbox. Some locations can have other rooms inside them e.g. Bedroom, inside cupboard, under bed. Keep that in mind when designing your locations or "rooms".
"Objects" are the fun elements of stuff to find or use, swap, trade etc. to progress in the game. Try not to duplicate objects e.g. Mirror and window are both made of glass. You will have some issues if a player "looks at glass" and it exists in 2 places! There are ways round this, but for the sake of an easier fun game creation, avoid these little problems if you can. Just open up Google and find alternate names for the same object is very helpful I found.
"Characters" are helpful for giving clues to players or giving and receiving objects. It is fun making up replies they say to when players "ask character about objects or things". You can also give objects to characters and make them give / swap an object. This makes for interesting tasks to achieve in the game.
The forum is helpful. Use it if you have any problems. There are a lot of people here willing to help. Have fun.