Documentation for Office: The Document Foundation maintain a full set of documentation here.
Mailing Lists: The Document Foundation operate the user support mailing list: firstname.lastname@example.org. It is the main channel for LibreOffice users needing help with a problem. You need to subscribe to the list first before you can post a question. To do that, just send an empty message (no subject line, no message body) to email@example.com. Instructions will be mailed back to you immediately (check for new mail, and check your spam/bulk mail folder just in case). In order to unsubscribe send an en empty message to firstname.lastname@example.org . Non-English speaking users: Native-Language projects have their own users mailing lists. See here.