After opening the NML Wiki in edit mode, navigate to the Pages tab in the editor menu pinned to the right of the Google Sites interface. Right-click the Tutorials page in the list of Pages, then click Add subpage. Name your tutorial subpage something fitting.
The new subpage should populate immediately. It will automatically have a header banner that is the same as the header on the main Tutorials page, and a title in the header that is equivalent to whatever you named the page. Adjust both of these things so that they are more appropriate to your tutorial.
By default, the new page will populate in any dropdown navigation menus related to the Tutorials main page. However, since many of the tutorials may be "ad hoc" (particularly initially), the sub-page will probably go directly under Tutorials unless it clearly belongs to one of the "non-hidden" sub-headers. It will therefore be cleaner if your sub-page is linked to from some element within the main Tutorials landing page as opposed to from a dropdown navigation menu.
Right-click your new tutorial sub-page in the Pages menu and select Hide from navigation in the context menu. This prevents the page from showing up as a navigation sub-item under the Tutorials navigation link. A page icon with a slash through it as pictured below indicates that you've done this part correctly.
Add content to your tutorial. It is helpful to include images similar to how they are arranged in this tutorial (you can use this tutorial as a template by clicking Duplicate Page in the context menu in the Pages menu on the right). To add more panels similar to the layouts used in this tutorial, use the highlighted section Layout from the Insert tab of the editor menu on the right, as shown in the image.
To change section colors, use the color palette context button that populates when you hover over a given section panel as shown below.
To ensure that other lab members can make use of your tutorial without needing to navigate onto the wiki editor, you should make sure there is a link to it where appropriate on the Tutorials landing page. Navigate back to the Tutorials landing page, and add a link as appropriate (for example, to the text and new image in the content placeholder shown to the left). If you are able to add an image related to your tutorial, be sure to link both the text and the image to the tutorial page by clicking the link context button and then typing in the name of your tutorial sub-page, then selecting it when it pops up in the text auto-fill menu.
In general, the Tutorials landing page should be kept in a state where it is clear that other lab members would like some kind of specific tutorial to go, so it is a good idea to check the Tutorials page beforehand if you are considering adding information but not sure specifically what to add information about. If there is no obvious place where content for your tutorial should be inserted, but you have a specific thing you really want to add a tutorial for, consider adding a high-level heading to the Tutorials landing page. See existing headers when considering the specificity of a new header. Finally, add one of the section layouts with placeholders so that others can see where there is missing information. Thank you for contributing to the NML Wiki tutorials!