Got a truck or a van?
What supplies do you have now?
What equipment do you have now?
How much experience do you have with detailing now?
I started with a bunch of stuff from walmart like turtle wax polish, Meguiars NXT 2.0, some touch free tire shine, some Tuff Stuff cleaner, some dollar store micro fiber towels and a crappy wax spreader polisher. I had a digital camera and some Avery business card paper from wally world. Made up a cheapo sign with magic marker and started shining cars for money. I quickly learned that I would need to invest some money in some real equipment but I had no money, just a desire to succeed and a willingness to work 2 full time jobs. My day job and waxing cars until I got enough for my first polisher. I put 50% of all my earnings back into growing my tools and products/supplies. I took pictures before and after along the way so I would have something to show potential customers what I could do. As I gained experience I was better suited to speak intelligently and confidently about what I was trying to sell. People said "you'll never be able to make this work" And "you aren't charging enough, you couldn't be a professional." I learned from all the hurdles I had to overcome growing this venture with no working capital and made adjustments along the way. 5 years later I still have no working capital but I have a fictitious name, business insurance, a mobile rig, a brand new to me fixed location shop and a ton of money spent on a ton of products and tools that didn't work out in the end. I have a lot of tools that do work out though and have weeded out the products that didn't work and have settled on a few staple products.
I did all this and continue to do this while working a full time day job. This is the hard way but the scoffers said it was impossible. I guess they were wrong.
Give us some insight as to where you are presently with your desire, tools and products and you'll probably get better feedback.