Hi,
A go to market strategy (GTM) is a plan which shows how you plan to penetrate the market with your product / service.
Among other things, you need to explain:
1. Who is your target market? (Be accurate).
2. What marketing methods do you plan to use to reach them (and why you chose these platforms). .
3. How much will these methods cost (you can to a test on FB or Instagram or whichever platforms you plan to use)
4. What % of your target market do you expect to reach and within how much time? (be realistic).
"How can I create one":
1. Hard work and research.
2. You can find examples online (here are a few:
https://blog.upscope.io/10-companies-show-you-their-go-to-market-strategy/
https://theproductcompany.com/gtm-strategy-examples/
https://www.byteant.com/blog/go-to-market-strategy-for-startups-a-complete-guide-free-template/

Good luck