Hi. I love talking to new archers! We've all been there and we all needed help. Some of it was good and some of it was well meant but they didn't know much more than WE did.
To start with, a "bag" is a target. It's typically a large bag filled with stuffing and it has a target printed on it so you have something to aim at. They are pretty reasonable - some as low as $20 or so around here anyway - and they work pretty well.
Being a mom, the first "problem" I can see with you setting the bag at the end of a hall is, a beginner isn't always going to hit the target (bag) and I can foresee some pierces in the wall that some one
is going to notice!
Do you have anyone that you can talk to locally? Is there a sporting goods store or shooting range in the area where archers might hang out? You can learn a lot by just listening to other archers.
If you're still in school, do you have a 4H group that teaches archery? My husband and I coach our local 4H archery group and we have all ages and experience levels. Does your school have NASP - National Archery in the Schools Program? What about a Boys Club or Scout group? Anything like that? Big Brothers??
If all else fails, we'd love to share what we know with you.