A match is won with two panels. Every island wears an island panel telling you who holds it and how many troops are there, and the islands linked to the one you selected get a forward panel for sending your troops. Here is what every part of them does.
Pick an island to claim it as your own before the competition starts.
Your armies grow over time on every island you control.
Move your army toward a rival island to attack, or toward your own to reinforce it.
Wipe out every rival army and occupy all islands to win the match.
Every island wears a panel telling you what is there. Click one of your islands to select it: its panel grows and gets an outline.

The troops on the island, and how many it gains per second.
Who holds it: You, a rival, or Unoccupied.
The island’s number.
Other islands show the same panel, smaller. Check a rival’s troops before you attack.
With one of your islands selected, every island linked to it gets a forward panel next to its island panel. That is where you send your troops.

How many troops to send: all, three quarters, half or a quarter of your selected island’s army. The bright one is picked.
Go sends them now.
Auto keeps sending that share: a new wave each time the last one has landed. Click it again to stop.
The troops defending this island. Send more than this to take it; sending to your own island reinforces it.
Who holds it.
The island’s number.