A processor is different from an effect because it has no wet/dry dial on the interface. This means the audio that comes out of the processor is changed, where as with an effect the wet/dry dial determines the amount of effect added to the original audio. Example of a processor is compression.
An insert is what you would use if you wanted to add a processor as this changes the audio directly rather than adding something to the sound. A send/return is what you would use if you wanted to add an effect, this allows you to add an effect like reverb to multiple channels by turning up the correct send knob.
The way I did this was to choose the processor I want to use and drag it into the gray box under the session for that channel.
