Here is the info you requested:
The most common filename extensions for files employing JPEG compression are .jpg and .jpeg, though
.jpe, .jfif and .jif are also used. The file extension
does not matter as long as it is in Joint Photographic Experts Group standard. That's what they are looking for.
Regarding your 2nd question, as long as you did not borrow the camera from some museum to take your picture, you should be fine. j/k.
When you save your image as jpg, jpeg etc, the standard format is that it
is saved in 24-bit color.
(They know not everyone works for Adobe and what they are asking for is pretty simple.)