There are two options to posting pictures and they both have their pros and cons.

Option 1 is adding a picture as an attachment. To do this you would select the "Upload attachment" tab below the post's text box. You then browse for where the photo is, select it and hit the "Add the file" button.
Pros:
You don't have to have the photo hosted online. You can upload directly from your computer.
May be easier for you to use as you don't have to deal with BBCode.
Cons:
The photo will not be viewable in your post unless someone clicks on the attachment.
If the photo size is huge on your computer it will be huge on your post.
You can only attach three pictures per post.

Option 2 is adding a picture using the image tags.
Above the post's text box you will see little buttons that all insert BBCode into your post. The image tag button is the one that says "Img" on it. To insert a picture this way you would hit the button and then this will appear in your post (without the asterisk): [*img][/img*] What you would the do is post the pictures URl in between those two img tags, like: [*img]http://farm4.static.flickr.com/3187/2912578392_98e4747e6e.jpg[/img*]
Pros:
If you use a service like Flickr or Photobucket your photo's size can automatically be decreased by the website, so you don't have to do any editing.
Your picture will automatically show in your post; no one has to click on it.
No limit to the amount of pictures you can insert into your post.
Cons:
You have to have some way to host your photos online.
You have to take the time to upload the photos from your computer to the online host, and then image tag them here.

Examples of each from our site:
Attached photos
Image tagged photos

If you're hesitant to sign up for an online photo hosting account I will probably be starting a group Flickr and/or Photobucket that we all can use to host our pictures of get togethers and our pets. So, let me know if that's something that would be of interest to you and I'll see how I can supply everyone with the username and password to use the account. And just a note, I'll be doing this with YouTube, too.