How do I wire an AC SSR with RAMPs 1.4?
If you take a kettle lead with a wall plug and cut off the other end, it will expose 3 wires: earth, live and neutral. These are color coded depending on your country, usually earth is green (possibly with yellow stripes), neutral is blue, black, grey or white and live is brown, red or black.

The SSR should have 4 terminals: 2 terminals for the switched load (which are interchangeable) and 2 terminals that connect to your electronics, which should be marked negative and positive. These terminals should connect to the negative/positive heated bed output of your electronics. The terminals of the SSR should be clearly marked, and you can verify which terminal is what from the SSR's datasheet.

Typically, your heated bed will have two wires for power (which are interchangeable). One of the wires should be connected to neutral. The other wire should go to one of the load terminals of the SSR, while the other load terminal of the SSR should connect to the live wire. It is also acceptable to do it the other way around (neutral to the SSR and live directly to the bed) but this is slightly less neat.

Finally, and this step is extremely important, the earth wire of the plug has a protective function: should something fail, metal parts of your printer may become electrified, and shock you when you touch them. To prevent it, you should electrically connect exposed metal parts of your printer (such as the frame, heated bed plate, power supply case, etc...) to earth. This provides a path for the current to flow (and trip the protective RCD breaker) should something go wrong.

I would further recommend that you protect your heated bed (particularly if it is a high power model) with a bimetallic thermal switch. These are available in a variety of ratings, and will switch the power to your heated bed off when it goes over a certain temperature. This switch should be wired between the relay and the heated bed, and be mounted on the heated bed so it makes good thermal contact. If you plan to print with the heated bed at 110C, you might get a 120C or 130C thermal switch.

As mains voltage can be deadly, you should take appropriate precautions: never work on the printer while it is plugged in, cover any connections (in particular, make sure you buy or print a cover for the SSR's terminals and wrap solder joints in heat shrink or electrical tape) and always treat wires coming out of the SSR as live (even if it is switched off, some current can still flow).