You don't need to "activate" it per se. You will, however, receive 6 months at a time stamp once you land. Make sure to present this either in printout or SS
I think it'll be helpful for you to have target countries or cities. For example, Hanoi still is one one of fastest (although they became stricter since I got my visa last month - March). Look into posts about Hanoi, HCMC, Jakarta and Manila. Best of luck!