Here are a few tips to point you in the right direction
Do Not Quit....Yet!
First and foremost, if you are currently working full or part-time, do not quit your job.
Starting a business will take longer than you think it will.
Starting a business will take longer than you think it will.
Describe your product
Describe your product and/or service concept in as much detail as you can. Clearly articulate the value and advantages "you think you have" for your customers. Your concept should be based on solving a problem for customers.
Target Customers
Identify your target customers. Make sure the target market is large enough to enable your business to grow.
Test Your Concept
Find potential customers to talk with about your concept before getting too deep into development. Get their feedback and use it to refine your idea. This is where you must prove that the value "you think you have" will actually solve customer problems. Potential customers must see the value.
Competition
Identify and analyze potential competitors and alternative solutions. "But…, we have no competitors!!" is not acceptable!
Market Opportunity Verification
After you have verified there is market potential for your concept and that your solution is better than any competitor, incorporate your company.
Business Structure
Depending on the type of business you want to start, select the appropriate business structure. Some examples include Limited Liability Company (LLC), Sub-Chapter S Corp (S-Corp), Corporation (C-Corp), Non-profit, etc.. Research each business structure to see which one aligns with your vision. Each one has different tax implications. Business insurance should be considered as well.
More Detail
Define your product and/or service in more detail. If you are building a hardware and/or software product, create a minimum viable product to test with potential customers. Get their feedback and use it to refine your product / service.