Global quest is a series of contracts that are done by all seaport players world wide. When a „Global“ is announced in the in-game update news you will find the destination here

The tasks and rewards are balanced according to the level you are at.
You get instant rewards for each finished individual task (contract), as well as for all of the 5 stages that the Global Quest consists of. The reward for the fifth and final stage also includes one Gem for each task you have completed. You can see your total no. of tasks in two spots, a) when you open the destination, b) when opening your friends list.
The Global Quest consists of 21,350,000 points to be collected by all players, as soon as they are reached you cannot complete any more contracts, and if you were in the middle of one but did not collect the reward, that one is also lost and unfinished (nevertheless you will still be able to collect the reward for the last Global stage including your Gems until the end of the event).

a1 countdown; a2 completion of stages; a3 number of currently active personal task; a4 always collect immediately

Further to the Global Quest there is a personal achievement, to be found when choosing the event tab of your achievements (see pics). The Magic No. is 102 contracts in total which YOU have to complete in order to finish this 3x3 stage achievement (stage 1 – 2, 4, and 6 contracts; stage 2 – 8, 10, and 12 contracts; stage 3 – 15, 20, and 25 contracts).

Tip: Towards the end the last Global stage usually moves at 150,000 to 160,000 points per hour. So watch the countdown carefully!