Some of this is just links to LiveJournal FAQ entries. However, a) the LiveJournal FAQs are quite helpful and 2) the LiveJournal FAQ index is Long. So I'm linking just the most critical entries for the beginner here.
To add any other user, replace exampleusername with their username.
Commenting: Adding a reply to a post, or to another comment. Although it can be disabled, by default most posts accept comments by all users.
Communities: a multi-user journal. You can 'watch' a community, the community equivalent of friending. Community posts will appear on your friends page, and you can comment to the posts just as you can to a user's posts. You can also 'join' many communities, which will allow you to create posts on it. Watching and joining are not the same thing; it is quite possible to join a community without watching it.
Friending: the act of adding a user to your friends list. Users are not obliged to friend you back.
Friends list: a group of users whose posts appear on your friends page. By default they are authorized to read any post you 'friends lock'.
Friends-locked (also 'flocked'): Posts made to your journal can be marked as Public, Private or Friends. By default, any post marked Friends can be read by anyone on your friends list. You can only view a friends-locked post on another user's journal if they have you friended. Posts made to communities can also be friends-locked; you can only view those if the community moderator has friended you back.
Journal: where a user's posts appear.
LJ: an abbreviation for LiveJournal.
Posting: creating an entry in your journal, or in a community journal of which you are a member.
Recent Entries: see Journal.
Style: the physical appearance of an LJ page.
User Info: a very useful page. On your own User Info page you'll find links to many of the Journal management and LJ help pages. On other users' (and communities') Info pages are information about the user, and the links to friend them (and join a community.)
User Name: the name by which you can access any Journal. Note: this has the potential to be very confusing to a new user! For example, if you go to the User Info page for community_promo you'll see that the User is community_promo, but the Name is 'LJ Community Promotions'. Although some people might know a journal or community by its 'Name', the User Name is community_promo. This is the name you always want to use when writing to anyone who might not be familiar with the journal, so that they can find it.
Users: the owner of any journal.
One thing that does stay consistent throughout LJ is the userinfo/username link. Community links look like:
Clicking on
or
takes you to the 'user info' page for the community/user.
Clicking on the exampleusername takes you to that user's Journal page.
You can easily create links like this in any post or comment using the following LJ custom tags:
For users, enter: <lj user="exampleusername">
For communities, enter: <lj comm="comm_news">
I also provide the 'direct' links to several of the pages listed below, in each case replace exampleusername with the name of the user or community.
Calendar View (aka Archive, aka Calendar): a calendar representation of the posts in the journal. Link http://www.livejournal.com/users/exampleusername/calendar
Friends: the user's friends page. Link http://www.livejournal.com/users/exampleusername/friends
Leave a comment: brings up a page to enter a comment on a post.
{n} comments: brings up a page displaying all comments on a post.
Recent Entries: the journal page. Link http://www.livejournal.com/users/exampleusername/
User Info: the user (or community) info page. Link http://www.livejournal.com/users/exampleusername/info