We recommend that new users read our Mission Statement, and rules in order to gain a better understanding of our goals. However, once you've done that, here are some things to help you get going.
If you want to create a new article, there are two ways to get that going. One way is, if you're reading an article that contains a "red link" (text highlighted in red text), that's a link to an article that has not been written yet. You can start writing that article by clicking on the red link. Otherwise, look up at the tool icons at the upper right of the window; the one that looks like a piece of paper with a folded corner is the "new article" icon. Click on that, enter your proposed title (it will check to make sure an article with that title doesn't already exist), and off you go. You can edit an existing article by clicking on the word "Edit" above and to the right of the article text.
There are two editors, known as the "source editor" and the "visual editor". We recommend that new users use the visual editor. If it opens with the source editor (it will say so above the header bar, to the right), click on it to get the pop-up menu and change to the visual editor. Then, start typing! Here is a link to the Fandom Community Page, which will point you towards more instructions for using the article editors.
A key to the value of any wiki is links. Whenever a reader is reading an article, and they see a term that they don't know, they should be able to click on a link and go to an article that describes that; this cross-linking of information is what makes a wiki useful and interesting. Whenever you open an article, Fandom checks all of the links in it to see if they point to an existing article. If so, the link is highlighted in yellow; if not, it is red. This happens automatically; whenever you create an article, all other articles that have red links pointing to that article title will have those links in yellow the next time they are viewed.
To create a link in an article you are editing, highlight the text that you want to link, and then click on the tool icon that looks like two chain links. A dialog box will appear, where you can find the article you want to link to. It will initially take the text you highlighted as what to search for. This may or may not be the actual title of the article you want to link to. If it is, you're good; click "Done". It it's not, it will try to find a close match, which may or may not succeed in finding what you actually wanted. (A particular problem area, for some reason is plurals; if the text you want to link is the word "mixers" and there's an article called "Mixer", it probably won't find it.) If the search doesn't get what you want, you can change the search text until you get it to find what you want. This won't change the highlighted text in your article; it just changes what the search searches for.