Userlevels
For a complete list and description of the user levels see Plus Forward - Userlevels.

User Profile
To modify your user profile first go to the profile page (top right user menu -> profile), click on the down arrow next to your username to bring up the user options and click on edit profile. Make sure to set a proper timezone since all times on the site are being converted to this timezone.

User settings
The user settings can be found via the user menu under "settings". Here you can disable reply notifications, change the comment indent indicator colors, the site theme and the default position of the quick filters (open/closed). In the settings you can also change your personal site wide category filters (tho they are overridden by quick filters if they are active).

Contribute
To contribute new posts click on "contribute" in the user menu and then pick the relevant post type for your contribution. Depending on your user level your post and attached files will have to be approved by an admin first. If you wish to get assistance with your post pick the fitting option in the select menu for "Req. Assistance".

Commenting
The site supports comment on almost every post type and provides a reply thread system similar to popular sites like reddit where the latest comment isn't automatically at the end but is appended to whichever comment it is replying to. If you wish to reply to a comment make sure to click on the reply button (curved arrow icon) in the top right of the relevant comment. Depending on your user level comments and attached files will have to be approved by an admin first.

iMsg
To send an iMsg to another user either click on "iMsg User" comment option or simply open the new iMsg page and enter the user name you wish to message. Plus Forward iMsg's are not permanently stored and get deleted 2 weeks after having been read.

Bookmarks
You can bookmark any post on the site by using the "Bookmark" option in the post menu. You can find your bookmarks by opening the user menu and clicking on "Bookmarks".