Can we withdraw money from our flex account at the end of the year? or lets say use it for online purchases?
And if we transfer to another university next year what happens to the money ? :o

you can request to get you flex money back at the end of the year or it will just transfer over to the next school year, if you are still at school.

You can not use your flex account for online purchases or purchases at Titles for instance.

This is what it says on the McMaster site:

The FLEX account is an optional account that allows you to continue non-taxable purchases of food on campus once the Basic account is exhausted.
The FREEDOM account gives you ability to purchase non-food items on campus and to dine at the participating Off-Campus vendors. All purchases made from the FREEDOM account will be subject to the appropriate taxes. At any time during the academic year, you can deposit into the FLEX and/or FREEDOM account or transfer monies between your FLEX and FREEDOM accounts. Unused funds in the FLEX and FREEDOM accounts will be automatically carried over to the next term or can be refunded to you.