What is Nextcloud and why should I use it?
Nextcloud is a cloud file storage software solution.

Pros:
- Nextcloud is self-hostable.
- Nextcloud if Free and Opensource.
- Nextcloud is reasonably easy to set up.

Cons:
- Nextcloud requires some setup.
- Nextcloud is not as well-integrated as some other commercial solutions.

Other considerations:
Nextcloud, being Free Software, is more private than commercial solutions.
File sharing in Nextcloud only exits between users on the same network.
There are many integrations into the Nextcloud system which are available as apps, including office apps, calenders, email clients, and much more.
Hosting a server requires some basic linux command-line knowlege, as well as a general idea of how the web works. Following a tutorial is possible, but as a server administrator, is is advisable to know what you are doing.
You said Nextcloud is Free, do you mean Free as in Freedom or Free as in Gratis?