well to build score you need to either increase power gain crystals or relics.
To get power you need to build units, get more workers or conquer players.
What gives power:
25 workers = 1 power
10 inf = 1 power
10 vechs = 2 power
10 tanks = 3 power
1 conquer = 1 power
1 metal mine/oil well = 0.2 power (for each one you alliance owns)
20 score per crystal
1000 score per relic
As for your 2nd question I am not sure i would be able to answer that
And the reason why someone has moved is likely to get out of possible danger or move closer to his teammates.