what is Confluence it is necessery to purchase

[Udo Brand]

see here: https://confluence.atlassian.com/display/DOC/About+Confluence

no, you don't need to purchase it if you don't want to use it (even if it is a great product).

[Nic Brough -Adaptavist-]

There's not a lot in the way of a useful question here.

If you want to use Confluence, then buy it (either Server, Cloud or from a 3rd party managed service provider, depending on what you need).  Bear in mind that if you want Team Calendars and/or Questions, you need Confluence to support them.

If you don't want to use it, then don't buy it.