1) To close the "active application"
a) Double Tap the "clock"
b) Tapping and holding the "clock" at the up-right corner (2-3 sec) or
2) Tap on the "clock" at the up-right corner, will show X2 and a list of running applications.
3) Tap and hold any item on the list of running applications in the task manager, will give you the option to close all running apps.