First off welcome to Olympus! It will definitely take some time adjusting from the switch, but with time you will learn to love Olympus and Arma 3.
In reference to @ SheriffJohnBeard he brings up many great tips, including that Staff and Support Team are here to assist you if the need arises.
My biggest tip would be to join a Gang! We have a lot of great resources to find a group to play with including the Olympus Forums, Discord, and even the Ingame recruiting menu. Not only will it help your transition to Arma, but it will help you learn the ropes of Olympus while also giving you extra players to rely on when attempting to complete a run, event, or fights along the way.
Here are some of the necessary links that he mentioned in his tip list that will provide help along the way.
Teamspeak IP:
Discord Link
Olympus Wiki (literally the greatest tool we have)
Olympus Support Ticket Tab
Have fun and feel free to reach out if you have any additional questions!