I'll start with the basics that will apply to much that you do when formatting a forum post.
If you are quoting or including an image or doing any special formatting like bolding, italic or colors, you're using what is called "BB Code". It works sort of like HTML does, and it's not complicated, but it does have some very specific rules. You don't have to follow the rules... but your formatting will be all jacked up and things won't work right if you don't!
First and foremost, BBCode is a "tag" based language, and every segment of text that you apply a tag to must have an OPENING and a CLOSING tag. If I try to show you the tags here in this post, they will be interpreted and you won't see the raw code, so I will add spaces between the brackets and the tag here to demonstrate. When you actually use the tags, omit those extra spaces.
Bold Text Example
To generate bold text, you use the [ b ] tag. It will look like this: This text is normal and [ b ]this text is bold[ /b ].
Note that the closing tag has a slash before it. That is the common format that you will use. It applies to any of the BBCode tags.
Quoting is one that messes a lot of people up because often when you quote a message, it has "nested" quotes. That is, a quote within a quote. And if you try to edit that, it's easy to mess things up. Which brings up another fundamental rule: Tags cannot overlap.
Tag Overlap Example
If you need to do something like make some text both italic and bold, for instance, you would NOT do it like this:
[ i ]This is italic, [ b ]this is bold italic.[ /i ][ /b ]
That is invalid because you've tried to close the [ i ] tag before closing the [ b ] tag that is within it. Bad form.
Do it like this:
[ i ]This is italic, [ b ]this is bold italic.[ /b ][ /i ]
No overlap. The [ b ] tag and it's closer are completely wrapped in the [ i ] tagged text. Nesting it okay. Overlapping is not.
More about Quoting
Now that you know all of that, you can do some fancy quoting. The [ quote ] tag has an "attribute" that you can use to say WHO you are quoting. To use it, you simply say [ quote="Name" ] and your quote will appear with that name on it. It's good to do that for at least the first quote of your message. If the remaining quotes are from the same person, you can just use a generic quote tag.
Quoting Example
The below is a quick exchange between you and Joe. You're quoting Joe's text.
[ quote="Joe" ]What color is the sky?[ /quote ]
The sky is blue, of course.
[ quote ]And how long has it been that way?[ /quote ]
That depends on who you ask, Joe.
If you enter that without the extra spaces, it would appear as:
The sky is blue, of course.Joe wrote:What color is the sky?
That depends on who you ask, Joe.And how long has it been that way?
Pro Tip
To check your formatting, use the "Full Editor" and click the "Preview" button next to the "Submit" button. You'll quickly see if your formatting is correct before you submit the message. Of course, if you don't catch it and notice errors after you submit the message, you can always edit your post and fix it.