I'd venture that if you have to ask such a generic question about how to start a startup, you're probably not well equipped to do so.
My suggestions are as follows:
1. do 3-6 months interning with a small very early stage startup
2. find someone else to execute your idea whilst retaining a % equity
3. look to find co-founders who can execute the idea, stay involved but focus on your skill set (if it's relevant)
This is a very wide question.
Is it just an idea? What level of market research has been done? Is it "more" than just an idea? Assuming it's all going to work out, do you have a plan to move forward? Any crude budgetary numbers in place?
And many more questions. So it's impossible to answer your question.
Spend as much time as it takes to come up with answering this question..Why would I buy your product or service? This will give you your USP. From there you will develop your drive, your, passion, and your marketing voice. From this you will develop unstoppable perseverance for success.
Best of Luck,
From the Trenches to the Towers Marketing
I will be glad to help as my time permits.