I’ll try to answer questions with a couple links:
A personal journal is what you sign up and get to write in. Your posts show chronologically, newest at the top of the page. Some people use their livejournal like a message board, but because it is meant as a blog/journal, new comments don’t bump up threads. At the bottom of each post there are the comment links, for making comments or reading them. As you can see a few posts down, it is possible to post pictures using the <img> tag, and many people host their pictures at http://www.photobucket.com for that purpose.
As for who can comment: You can specify in your setting who can comment on your posts in your journal. Some people don’t want comments from anyone they aren’t familiar with and set it to “friends only” comments. That means nobody can comment on your posts unless you have listed them as a friend. You can also make commenting available to any LJ member, and choose to allow or disallow anonymous comments from people that might not have an LJ themselves.
The real fun to LiveJournal isn’t posting though, at least not for me. It’s READING. Now, you could check people’s individual journals all the time to see if they’ve posted anything new, but the easier way to do it is with your friends list. When you stumble upon a journal you like and want to keep up with it, you go to their userinfo page. Most journals will have a link somewhere on the main page, or you can go to http://www.livejournal.com/users/THEIRUSERNAME/info
This userinfo page shows their username, journal title, e-mail address if they choose to make it public, the people they list as friends, the people who list them as friends, by clicking the avatar on this page you can see all of the icons they use (free accounts get 3 I believe). It sometimes shows communities they belong to, an interest list, and a place for a bio.
On that screen, there is an “add to friends” button. It is a little icon of a person’s head with a plus sign next to it. By adding people to your friends list, they show up on your friends page . The layout here is different than the journal I posted before because you can customize the look of your “recent entries” page and “friends page” and everyone seems to have a different look. It’s nice having everyone on your friends page because it puts their posts in chronological order, says who posted them (with avatar), and it’s YOUR friends page so it’s YOUR choice of layout for easy reading.
If you have any communities on your friends list, it will show the community name AND who is making the post. So I can look at my friends list and say “oh, bob said this and jill said that and some guy named steve said something in the music_lovers community” all on one page.
As for posting to communities, you have to join them first. You get to a community’s info page/profile the same way as with any other journal. From the main page there should be a link, or go to http://www.livejournal.com/community/COMMUNITYNAME/info. You can join the community, be added to the member list, and have posting access, AND/OR add it to your friends list. You don’t have to do both. You can add a community that you want to post to, but not friend it because you don’t want to read it every day. Or if you’ll never post, you can just friend it and not be a member with posting access.
Finally, to post in a personal or community journal, on the livejournal menu bar at the top of the page (it says Journal, Manage, Search, Help, and About) there are dropdown menus. Under “Journal” it says “Update.” This is the update screen you can always use to make posts. There is a dropdown box at the bottom of the page that says “post to: __________” To post to your own journal, leave it as the default, it should say your journal name. To post to a community you are a member of, just choose it and it will post there instead.
And as everyone already said, there are a lot of modifications you can make to your journal. You have ONE username, and that’s what shows up when you make comments or community posts and what your friends see if they have you added and showing on their friends page, but you can title (and subtitle) your own journal and friends page whatever you like, and change the look and layout with a number of options and color schemes.
Journals linked were picked sort of randomly from my friends page. Hope this helps, even if it is a bit too step-by-step and overexplained. Most importantly, you should tell us your username when you get your LJ going so you’ll have people to friend you and read your posts, and answer any more questions that might come up later.
I mostly post pictures of my baby, things I’ve knit, things I’ve baked, and the occasional rant about politics or my HMO. Even though I like reading this sort of mundane stuff about other people, it’s always surprising that people are intersted in MY mundane stuff.
Maybe it’s a layout that isn’t available for free accounts, or something? I’m using the “Digital Multiplex” layout in the meantime, and I’ll be happy enough with it after I tweak the colors and stuff some more (I already changed the font).