Attached is an image much like the one already posted including the relay coil.
Before Contactor and SSR first let's look at Relays and Contactors. Generally speaking the term Contactor applies more to a high current device. Though the two terms are used interchangeable. For example a device used in a motor starter circuit where a large motor may demand hundreds of amps the term motor starter contactor may be used more often.
A SSR (Solid State Relay) is basically an electronic relay. It is not a mechanical device and has no moving parts. Also, and again generally speaking, a SSR only has what would be normally open contacts. We apply a small low current / voltage control signal to energize the SSR which handles a much larger current or voltage. The SSR is for the most part a Triac or SCR type device. SSRs come in many varieties with their choice for use based on the application.
Keeping it real simple a SSR is a solid state (electronic) switching device while a relay or contactor is a mechanical switching device.
Ron