I tried using [code] and [/code] but that doesn't work. I tried using the Code button but that didn't seem to work either (i.e. past code into editor, highlight, then hit the Code button). So how to add code tags?
BBCode no longer works for new posts, it's all Markdown based now. As far as making a code block, it's a matter of indentation (at least 4 spaces). Presently the code button only pastes an example into the editor if there's no text selected. To paste actual code, you would just paste it in, then select the entire block and hit tab or click the code button.
Another option is wrapping your code in ~~~, which will force a code block without the need for indentation.
I recognize that selecting the code to turn it into a code block is awkward, we're working on making the editor more convenient. ;)
I tried using the Code button but that didn't seem to work either (i.e. past code into editor, highlight, then hit the Code button).
I just tested and it appears to work properly. Can you reproduce the problem consistently with all options described above?
You need to put a new line before and after the code block. Unlike vBulletin's bbcode, Markdown is a more universal language used across many sites sich as Reddit, Github, etc. If you do a Google search for markdown tutorial or markdown documentation, you should be able to get a bunch of help.