Each article has its own talk page, which can easily be accessed by clicking the 'discussion' link at the top of the page. Discussions can be used to discuss changes relating to the article, or just ask miscellaneous things. To add to a discussion, open the talk page, then click either on the 'edit' or '+' link at the top of the page (the difference being that the '+' link doesn't add the previous discussions to the editing window, so you don't accidentally delete them).
Note that if the talk page doesn't already exist, you're automatically sent to the editing window, where you can type in your question or similar.
The following tags are mainly meant for talk pages, but can also be used on any other form of article:
 Indenting your answer
If you want to answer to somebody else's question, it is generally a wise idea to use text indents to clearly separate your answer to the previous question. To use them, add a colon (:) to the beginning of your sentence, i. e. :This is an answer. You can use more colons to indent more than once - this is used for longer discussions.
An important rule at AcmlmWiki is 'Sign your comments in talk pages'. To do this, add four tildes (~~~~) at the end of your message. This adds a link to your User: page, along with a timestamp. Note that you can also use three tildes to only display your name (and link to User: page), and five tildes to only paste the timestamp (i. e. when you're not logged in).