Just to start off with: I don't advocate buying RIGs from the cash shop. If you have the capital to invest in them you can make plenty of gold without spending your real money on pixels.
Play/Open: Playing and opening are roughly the same thing. If you you have a individual RIG you can open or play it by clicking on it in your inventory and then instead of clicking one of the buttons at the bottom of the window that comes up you click on a link within the image (it should be pretty obvious. For example when you do Neverland to play you click 'fly' but if it's not totally obvious just move your cursor around until it changes from the arrow to the hand). The only real reason people sometimes use play and sometimes use open is because some RIGs all you do is open them and then they spit out an item whereas others there's some kind of game involved in the item-granting process.
That being said:
Never open them. Why? Because while maybe if you are an extraordinarily lucky person you might possibly get an item that is worth millions you're far, far more likely to get an item worth significantly less than the RIG itself. So only open them if you like to throw your money away because in this gambling game the dealer not only stacks the deck they made up the rules of the game so you're obviously not going to win very often.
Victory: Some RIGs have 'victory' levels. If you play through until you become victorious but close instead of claiming the item you will end up with the victory-level of that RIG. Some people do this intentionally because victories can be easier to sell or be worth more than items you might get from opening the victory.
I do not advocate opening 'victories' any more than the standard RIG.
Hoarding: To hoard RIGs you must have some gold to start out with. This is one of those cases where you need to spend money in order to make money. But if you have enough then you follow a pretty simple procedure. When a RIG has been out for about two weeks (but is still in the CS) buy as many as you can/want (it's most economical to buy bundles). Wait one to three months after the RIG leaves the cash shop and then sell them (they should usually go up to about 1.5x what you bought them for initially in this time period). Rinse and repeat.
If you're interested in learning more about hoarding check out my guide:
The Solution to a Problem: A Guide to Hoarding