There are 2 ways in which an effect is applied to a signal. Depending on what you want to accomplish with the effect, you will either INSERT the effect or LOOP it.
Inserting an effect means that you want the signal to be completely changed by the effect, all you want to hear is effected signal. Typically the Effects you would use in such a way would be EQ, Compressors, Hum Cancelers, Noise Supressors, Pitch Correction, Mic and Amp Simulation, etc.
Looping an effect is best suited for effects that accentuate existing signal. A looped effect will produce a sound that contains a balance between "dry" and "effected" signal, which can be adjusted to suit your needs. Effects in this category are, Reverb, Delay, Chorus, Phase, etc.
To use an external effect unit as an insert, we will take advantage of the VS-2400 / 2480 Dir (Direct) Bus.
Step 1.) Press EZ-ROUTING.
Step 2.) Push F4 to get to the OUTPUT ASSIGN section.
Step 3.) Use your mouse or the ZOOM keys to select AUX A from along the top, and turn the Time Value Wheel to assign this output to a DIR bus (for this example, we will use DIR 1/2).
Step 4.) Push the CH EDIT (Channel Edit) button for the channel you wish to be effected.
Step 5.) Cursor down to the DIR section (to the right of AUX 8, below the EQ section), and activate either 1 or 2 (or both if the insert is to be stereo and the channels are linked).
Step 6.) Cursor up to the box that says MIX, and turn it Off. This prevents the audio on that channel from coming through the speakers. It will only travel out the DIR out to your effect processor.
Step 6.) Connect the Aux A outputs (1/4" outputs 3&4) to the Left and Right inputs on your processor.
Step 7.) Connect the Left & Right outputs of the Processor to a pair of inputs on the VS-2400 / 2480 (e.g. Inputs 7 and 8). These are now your returns, and you will hear the affected signal here. You may record these inputs (external effect returns) the same as any other inputs (e.g. as if you are recording a keyboard).