As Sam mentioned, the weekly card is good from Monday to the following Sunday, no other combination of 7 days.
The current week's pass is sold up until midnight between Thursday and Friday; after that, only the next week's pass is sold. In other words, the pass for Mon 4 February to Sun 10 February is currently on sale and will be on sale until Thu 7 February at 11:59 pm. Starting Fri 8 February at 12:01 am, if you buy a weekly pass it will be the one for Mon 11 February to Sun 17 February.
This timing means that if you are arriving on a Saturday morning, which is common for those starting their trip on a Friday evening from North America, you'll need to figure out the best ticket options for the remainder of the weekend.
The pass allows you to travel anywhere on this map (PDF) out to zone 5, i.e. the white and gray zones, except for Orlyval (train shuttle from Orly airport), Optile special fare lines, and SNCF train lines with reserved seating (i.e. long distance SNCF train rides to other parts of France).