Delay and reverb effects are both created by repeating a created signal, while reverb occurs in very rapid successions and is dependent on the sound itself to its decay and timing and can be random in response. Delay has much more control and is a reoccurrence of a signal at a controlled timing.
The sound can repeat multiple times and or be fed back into the delay unit creating a gradual decaying echo.
So a delay effect stores a signal for a period of time before sending that signal either back into the input creating feedback or directly to the output.
In a DAW, delay will often be used on a send track, This is to allow multiple signals to be sent to a single delay plugin. To achieve this we can create a bus in logic pro. A delay would very rarely be used on an overall mix.
By choosing the sounds we want to be sent to the bus we use the bus send knobs that appear when a channel has a bus send applied.
The effect then needs to be applied to the bus and set.
Delay effects will often have wet dry controls for this type of usage, when applied to a bus in the was there is no need for a dry signal as this will occur within the original channel the signal is being sent from. Wet is the amount of the effect that is audible so on a bus its common to have 0% dry signal and 100% wet