If you successfully explore charged locations, you get more experience points/coins or chances to get a collection item, depending on the talent of the friend who left you help. If you're helped by a friend with an energy icon, less energy will be required for that location.
Press a location on your friend's map to leave help. This costs 1 action point. Your help will give your friend a bonus for exploration. The bonus depends on your talent:
Accountant (coin icon): increases the amount of coins a player earns by 10%
Keeper (blue star icon): increases the amount of experience a player earns by 10%
Strategist (energy icon): reduces a player's energy consumption by 10%
Ranger (red star icon): increases a player's chance of finding collection items by 5%.
As a reward for your help, you will get coins and experience. You can also charge your friends' trophies to help them get more bonuses.
If you help your friends out like this, they'll return the favor.