Editing articles, that is to say adding new and changing existing ones, is basically really easy.
First of all, you need to register (don't forget to give a valid email address) and you are set to start writing or iron typos/misinformation out of old articles.
Secondly you need to see if the article already exists. That is done by writing the item's name to the search box and hitting "go". If it is an item you should always use the full short description, but leave the possible <glows> and (glows) out since the search engine gets confused from <'s and >'s and because by always using just the base short description you preserve a standard which makes life easier later on due to consistency. For example, if you would want to add an iron überknife known as Bestest (glowing) <chilling> <red glow>, you should only type an iron überknife known as Bestest.
Now, if there is no hit, then hit the 'create this page' link and get down to business.
Usually there is already an existing template for what you are going to add, i.e. a kind of a frame, which is used for many types of articles. E.g. Weapons, shields, armours, items (things that are mainly used from inventory), projectiles, spells, skills, different quest types, societies and plants all have their own templates. Simply copy the frame from the appropriate template page, paste it to the article and fill in the fields. The meaning of the fields are explained on the template page.
If an item increases a standard stat, for example intelligence or a skill, say, short blades, then it belongs to that category. To include an article into a category add e.g. [[Category:Int]] or [[Category:Short blades]] to the bottom of the article. Do note that items that reduce or hamper standard abilities are NOT categorized since then you couldn't use them to search beneficial things. Some special cases do exist though: Cursed item, restrictions such as Aura of blackness (aka. evil wear/wield only), and so on. If you're not sure how or what to categorize, searching for similar, already existing items can help. If you are still uncertain, you could either use the Discussion page of the article (for example Talk:A Vorpal Blade), ask people around (for example Nuane and BlackSmith are known to be active contributors to the site), or just simply leave it be and wait for someone else do it later on.
After looking through the preview to be sure the article looks ok (which you should ALWAYS do before saving), write what you did to the summary field, hit save and you have contributed!
There are also a couple of "oddities" you should be aware of. In 'description' field you shouldn't insert any additional rows, instead it should be all in one long row since the template automagically wordwraps them.
Also, when adding anything else and you need a line break, hit the enter once more, so that it has empty line between the two texts. This is the wiki 'languages' syntax to tell the wiki that you want a real line break. Test out <br> too.