The thing you're reading right now! The manual contains a wealth of information about OpenComputers (and possibly more). If you need information on an item or block in the mod, look no further! Scroll down to learn how to use (mouse wheel or the scroll bar to the right).
Navigating the manual is similar to browsing a wiki: click on links (1) to follow them to the page they reference. Right-click or press the jump key to go back one page. Press escape or the inventory key to close the manual. To the left you will find a few tabs (2) that provide a way to quickly jump to select pages, such as the block and item index. To the right you will find the scroll bar (3). You can either drag it manually, or use the mouse wheel to scroll in a page.
The manual will remember the page where you last left off, when re-opening it. You can start over on the main index page by using it while sneaking. It is also possible to directly jump to a page concerning a block in the world by shift-right clicking the block with the manual in hand.
If you spot any mistakes in the manual, factual, grammatical or otherwise; or bugs in the mod, for that matter, please let us know via the issue tracker. If you'd like to contribute to the manual by adding content, get in touch via IRC or by creating a ticket on the issue tracker.