A relay is a device that helps microcontrollers or microcontroller based boards like arduino to switch on or off different household appliances like motors lights water heaters television and fans etc. Territories for local andor long distance calls.

Automotive Relay Guide 12 Volt Planet
When to use a relay. Relays are used where it is necessary to control a circuit by an independent low power signal or where several circuits must be controlled by one signal. A relay is generally used when it is required to control a circuit by a separate low power signal or when several circuits must be controlled by one signal. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. A reliable relays is the most important and as the copper width and weight will impacts the max current that can be flowed in the circuit the width of the layout should meet the current requirements. This is useful when sending emails to external recipients to avoid anti spoof and anti spam filters to drop the messages because they are not coming from a whitelist smtp relay. Trs is available in all 50 states the district of columbia puerto rico and the us.
The elecrow relay shield has the following points to ensure its usage. The coil current can be on or off so relays have two switch positions and they are double throw changeover switches. Reliable relays and layout. But it is theoretical we need to notice something in actual usage. They are very useful devices and allow one circuit to switch another one while they are completely separate. They are classified into many types a standard and generally used relay is made up of electromagnets which in general used as a switch.
Mounting holes are provided for easy installation to walls etc using screws. The main usage of the relay was seen in the history for transmitting and receiving the information that was called as morse code where the input signals used to be either 1 or 0 these change in signals were mechanically noted in terms of on and off of a light bulb or a beep sound it means those pulses of 1s and 0s are converted as mechanical on and off using electromagnets. Relays were first used in long distance telegraph circuits as signal repeaters. Although keep in mind you may have to pass credentials to use your isp or maybe even your enterprise smtp relay. A relay is an electrically operated switch. Telecommunications relay service is a telephone service that allows persons with hearing or speech disabilities to place and receive telephone calls.
Yes it is so easy to use a relay. They refresh the signal coming in from one circuit by transmitting it on another circuit. Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. Each relay can switch up to 10a at 14v dc or 10a at 125v ac for resistive load 6a at 14vdc for inductive load.