Hey there, @user1000
Bo here from Shopify Support!
That is a really great question. Shopify emails a bill every 30 days to the store owner. You can view your bill history as well as your upcoming bill date and any outstanding charges on your account from the Bills section of the Billing page in your Shopify admin. Payment for these bills is taken by the system, automatically every 30 days, you do not need to manually make any payment. I would highly recommend checking out our guide on Shopify Billing right here.
What is it that you are on selling with Shopify? I would love to know more about your business so that I can provide more specific resources to help you get started.
In the meantime, as you are getting prepared to launch your store soon I would definitely recommend taking a look at our Essential Shopify Store Launch Checklist before going live to make sure you don't miss anything. We also have this great Buyer Trust 101 post which goes through how to make your store more trustworthy to customers so that they will check out.
All the Best,