This is going to sound a harsh but it's the truth - if you want to start a business of any kind, and be successful at it, you also need to be the sort of person who can be proactive and driven and research information on your own. I'm sorry as I don't know if English is your first language which could make that considerably harder.
You need to go back to the beginning. Why do you want a store if you have nothing to sell? A Shopify store might not be the best option - depending on your products, a marketplace like eBay or Etsy might be better.
First think about what sort of business you want and what you want to sell BEFORE you do anything else! Are your products going to be physical things that you make? Or that someone else makes? Do you need to hold stock? Or will they be made/printed on demand? Or are you going to be selling digital downloads?
Once you have your product idea, you need to know if it's viable. Is anyone else selling them? How well are they doing? How are you different to them and why should people buy from you? Once you know how you're different, you can then think about who your ideal customer is. What do they live, how much money do they earn, what are their interests, which social media platforms do they use? You need this information to know how you will be able to reach them. It might be vague at first (I still don't have a clear idea) but it's important to develop your idea customer over time.
You need to work out your costs to sell the product(s), and then work out selling price that people will pay. Does that then leave you with enough profit? If not, you need to rethink your costs or your product.
With the internet, there is no shortage of free resources - websites, ebooks, You Tube, videos, etc. so spend time reading and watching and taking notes. You need to think about your current skillset, your strengths, interests...as well as where you might need training. Look at resources too - how much time, money and people power (in the help of friends/family) do you have? All very important considerations.
Once you have an idea as well as some more background info on starting a business, read the help pages and watch the Shopify videos...THEN when you have questions about specific things, come back and ask the community. And once your site is setup and business running, you'll need to invest maybe 80% of your time into marketing - there's a lot to learn here and it sounds like this is mainly what your question is about.
It's just too general an area to discuss without you even knowing exactly where you are in the process.
Good luck :)