The 16.3 MB PDF instruction document (Nikon calls it the “Nikon D3100 Digital Camera Reference Manual”) for the Nikon D3100 should prove to be a fantastic read, all 224 pages of it — be sure to download it.
Both English Language (printable and non-printable) and Spanish (non-printable) versions of the Nikon D3100 Guide to Digital Photography / Camera Owner’s Manual can be downloaded at NikonUSA.com.
For copyright purposes, the printable version of the Adobe Acrobat PDF document requires you to input your camera serial number and agree to a license, while the non-printable versions do not. You’ll get the following dialog box if you try to print the password-protected, non-printable document.
The guide discusses the features of the D3100 and how to use the camera, for instance, on page 177, there’s an explanation that describes the use of optional Nikon GP-1 GPS Unit and Nikon MC-DC2 Remote Release Cord accessories which plug directly into the accessory terminal that’s located on the left hand side of the camera body.
Other types of devices can be plugged into the accessory terminal — one example is third-party RF (radio frequency) remote control units such as the Phottix Cleon N10, Phottix Plato and Phottix Cleon II.
Nikon D3100 – Main page