Atlassian owns Jira, the product that powers Jira Software, Confluence, and other Atlassian products. If you have a Jira account, you have a Jira Software account. If you have a Jira Software account, you have a Jira account. If you have a Jira account, you have a Confluence account. If you have a Confluence account, you have a Jira account.
Jira Software is a product that Atlassian sells. It's a commercial product. You can use Jira Software for free, but you can only use it to build your own software or services, not to build the software or services that you sell.
You can build software or services that you sell on Atlassian products.