The symbol means that it's a DPDT (Double-Pole, Double-Throw) relay. That means that, internally, it contains two separate switches, each of which has two positions.
Pins 1-3-5 are the first switch. Pin 5 is the "common", which is connected to either pin 1 or 3. Those diagrams always show the relay in the de-energized state, so when the relay is "off", pin 5 connects to pin 1 (The "normally closed" pin), and when it's "on", pin 5 connects to pin 3 (the "normally open" pin.)
Pins 2-4-6 are the second switch. 6 is common, 2 is N.C., 4 is N.O.
Pins 7 and 8 are the coil. When you apply 24 VAC across those pins, the relay turns "on."
The note at the bottom tells us that the contacts are rated to carry up to 30A at up to 250 VAC.
Here's a full datasheet: http://www.manhua-electric.com/Produ...Product_ID=841
To be honest, relays of this type are all pretty much the same, quality-wise. They're all made as cheaply as possible by slave labor in Asian sweatshops. I can't find any from the usual domestic suppliers, just get the one from Ebay. http://www.ebay.com/itm/JQX-30F-2Z-D...ht_2573wt_1396