You must get to the gateway in game. Not in cloudview. You must see it on the actual gameplay screen. Tap the gateway and when it's info pops up, tap the potion icon to the right. It will take you to a purchase menu for the gateway. You must pay 10 potions if it has not been purchased. If someone has purchased it, you must pay the value the person put into it plus 10. If it is bought from you and you have put 100 potions on it and the person put another 100 on it, the value is now 200. Anyone else buying it will have to pay 210 potions to buy it, but you will only need to pay 110 more as you have already paid 100 potions into the gateway value. First person to 5000 potions on the gateway owns it outright and it cannot be taken from you.

Hope that was sufficient and not confusing.

If the beacon runs out of power, destroy an item in your list of power consumers to gain more power. Generally, you put a beacon up with the intent to use it regularly, so you should be able to keep track of it unless the opposing team takes it out. Then you're screwed if you have no way back.

Sorry, can someone explain to me the advantages of "buying" a gateway? Or updating it to Bronze, silver, gold with the mana bottles?

For the moment, your name on the realm is bragging rights. In an update there is supposed to be bonuses for owning the realm and for what level it's at. I think at the moment there is a slight bonus to harvesting points if you are local and are on the team that owns the realm.

Ok. Thanks. I tried looking at the help page but didn't see any reason to "bid" on the gateway other than the game was telling me i could.

Currently you get minimal harvest bonus from realm value. Not really worth it imho.