By example:
Assume you have a Feb use year. On Feb 1, 2003 you will get a new allotment of annual points; those must be used for a trip that takes place between Feb 1, 2003 and Jan 31, 2004, unless banked. You have until the end of your sixth month of the use year to bank 100% of your annual allotment of points. Thus, in the example, you can bank all of those points issued Feb 1,2003 if you do so by July 31, 2003 (or the last Friday of July if July 31 falls on a weekend). You have until the end of your ninth month of the use year to bank up to 50% of your total annual allotment; thus, in the example, you can bank up to 50% of your total points by the end of October. That is a cumulative total. If earlier in the use year, you already banked 50% or more of your points, you cannot bank any more at the end of October. By the end of the 10th month (November in the example), you can bank up to 25% of your points (again, a cumulative total; if you have already earlier banked 25% or more of your total annual allotment, you cannot bank anymore at the end of the 10th month).
Any banked points will then be usable for a trip that takes place from Feb 1, 2004 to Jan 31, 2005. If not used then, those points will expire Jan 31, 2005 and cannot be banked any further. Moreover points once banked stay banked -- you can't try to bring them back into the current use year.