Getting Started
When you get to your new site you may already be in the page edit mode, if not you will see the basic Google Sites Tool bar:
From this toolbar you can choose to Edit a Page, Create a new Page, Choose from more options and Share your website.
Editing a Page
Once you click on the Pencil icon to Edit the page you are currently viewing you will see the basic editing toolbar. Many of the options on this toolbar will look familiar if you have ever used a word processing program.
The quick edit options from left to right are: undo, redo, Font, font-size, bold, italic, underline, font-color, font highlight, insert link, number list, bullet list, increase indent text, decrease indent, left-align text, center-align text, right-align text, remove formatting, and switch to HTML mode.
Above the quick editing options are the menu options: Insert, Format, Table and Layout.
Insert is going to be a very useful option for you, from here you can insert all kinds of items such as: images, videos, Google drive files, calendars, horizontal lines, a host of "gadgets" and many other things.
A Word About Gadgets
You can view the variety of gadgets that are available at http://www.google.com/ig/directory?synd=open.
It is important to remember that many of these gadgets are created by private individuals and not by Google. This means that some may not work as explained. However, some are very useful and work exactly as advertised. Make sure you test your gadgets before expecting students to use or interact with them.
If you are interested in creating your own gadgets you can learn more about the development at: https://developers.google.com/google-apps/sites/gadgets/site_gadgets.
Format allows you to format text as headers or apply super and/or subscripts to text.
If you want to use Tables in your document, the table menu option will help you insert and format your table. Tables are very basic in Google Sites, but can be handy for certain types of information.
The Layout option will allow you to change the layout of each page.
**DON'T FORGET**
Don't forget to save your page after editing! Google will save a draft periodically, but you don't want to loose any masterpieces you have created! Click on Save in the upper right hand corner to save the changes you have made, and return to the basic Google Sites toolbar where you can add a new page.
Creating a New Page
You will definitely want more than one page in your website. Adding pages is simple; just click on the Create new page icon from the basic Google Sites toolbar.
Name your page, this is the name that will appear in the navigation, so you may want to keep the titles short. Next you can choose a pre-defined page template; to get a "blank" page that you can edit choose Web Page. You can experiment with the other template types to see if any of them are useful for you.
Next choose the location of your page. You can choose to put it at the top level - which means that all pages will display in a list in the navigation. Or, you can choose to put your new page "under" another page. This will create a "sub-page" of the upper page. You will have the option of displaying links to subpages on the "upper" page from the page settings options.
Once you have completed the settings for your new page click Create at the top left. This will create your new page, and bring you to the edit page window.