Questions about keys from a newbie

TF2 or CSGO keys are used for the same thing, open crates (TF2) or cases (CSGO) in each of them there is a very very VERY tiny chance of rare item (unusuals for TF2 and knifes for CSGO) and they usually worth allot
keys are also used as currency because allot of people buy them from the market, meaning that you can sell them at any time to get money
until steam allow money trades we need keys to trade "money"

CS keys or TF2 Keys are just some kind of trade currency that's often used. Keys get traded and sold on the community market because steam doesn't allow to trade wallet, and trading games for paypal can be risky.
ROW stands for Rest Of World, wich means the gifts are region-free and thus can be activated anywhere in the world.

ROW means that a game isn't locked to a certain country or a region (Russia, Brazil etc).

The intended purpose for CSGO and TF2 keys was to have them open crates from which the players could get rare in game items. But since their value is relatively stable, people started using them as trading currency (they are around 2 EUR/ 2.5 USD each).

Thank you guys for clearing that up