It could be one of the two things:
1. Is it protected by a storefront password? Your shop will have a storefront password that makes shops unavailable to see while under construction. When its ready for the public to launch, then you can turn off the storefront password by going into Settings>Online Store and Storefront Password and uncheck the 'Password protect your storefront'.
2. You listed the current plan as basic/per month so this shouldn't be a problem as it will have the online store that comes with this package plan. To view the plant type, you can go to Settings>Account and under Account Overview to be able to change the information you have there. More info: https://docs.shopify.com/manual/your-account/manage-account
Hope that helps in getting your store active,
Thanks for your reply, Alan.
My store does not have a section Settings>Online Store.
Perhaps that in itself is telling. How is it that I have a "basic" plan, but no Online Store?
For what it's worth, I've had an online store for years, and sold many items through it.
I'd really like to talk to someone from Shopify but that doesn't appear to be available to me.