It means something like “alright!”.
Yeah, you are correct to put the “i” in brackets, as it’s often not pronounced.
To give some context, here are times when I’ve heard it used:
-
By the driver when we finally arrived and pulled up at our destination after a long drive.
-
When we were finally breaking camp and setting out for the days hike.
-
When lifting something heavy together as a group.
-
At the end of an informal meeting when we’ve decided on the day’s gameplay.