Hands Placement

The standard finger position is the usual ASDF JKL;
keys.
Regarding the thumbs, the left thumb should rest over the Backspace
key and the right
thumb should rest over the Space
key. Both thumbs share the central
Enter
key.
Dual-Function Keys
Dual-functions keys are keys that combine a TAP key and a MOD.
Simply speaking: when a dual-function key is tapped, one get the tap effect of the key. When it's holded or combined with another key, it will act as a modifier.
Layers
Layers are extra «layouts» containing different keys that can be accessed temporarly when pressing the corresponding layer key.
That's like another Shift
that provides access to different characters.
To learn the layers quickly print the guide.