I will relate this question to writing. I've been asked several times, "How did you do it? I would love to write a book." When you look at the entire task of writing a novel, it can be daunting (to say the least), but when you break it down into smaller portions it can become obtainable.
The dream you have is to write a 90k word fantasy novel. You love the genre and you have many ideas, and would like to see it come to fruition. Congratulations! That's the first step.
Your dream needs one key step, a goal. When did you want to have your novel completed? With the new year coming, let's say (for example) that you want your novel to be completed within twelve months. The goal is the most important part. Without an end date, your desires will be pushed aside, making it more difficult to complete.
For every goal to be accomplished you will need a plan. To complete your novel, you'll need a certain word count to make it happen. For a 90k word novel, you can break it down further to 7,500 words per month. Still a big number? That is also 1,875 words per week or 267 words per day. That's less than ONE PAGE per day. That is a reasonable plan.
All the planning in the world doesn't matter unless your desire to implement the plan happens. Schedule a time to begin writing, and stick with it. I've heard such things as, "I have no time, how do you do it?" Easy. You make time. In order for me to write, I set my alarm an hour earlier each day. I can get my writing done while drinking a coffee and while my house is still quiet. Other people have written a novel while commuting to work on the train. A twenty minute commute each way, a page per day, gets the job done! Balance your goal with importance. How badly do you wish your dream to happen? Give something up, like television, or scrolling for endless hours on social media.
If you are passionate, and wish your dreams to come true, follow the four-step guide. It has worked for me, and I hope you have nothing but success with your dreams becoming reality.