2. Sharing files
You can share large files on this server using the Nextcloud app which you'll find on your dashboard. Here you can simply upload files. It's very similar to how Dropbox works.
If you don't want to use Nextcloud on a browser and you'd rather just have it installed on your computer or phone, take a look at the documentation on Nextcloud's website. It lists all the different ways you can access your files on different operating systems.

Now, the server has limited resources. Disk space is not free! So don't use this as your backup for your whole computer, and make sure to not upload anything fascist or oppressive as well.
Let me know how it goes!
Encryption
If you want to encrypt files on Nextcloud I recommend you use Cryptomator with it on your phone or computer. If you're on Linux, you can use gocryptfs as well.