Was given a Canon AE-1—what to check for?

[John Koehrer]

If you put a little tension on the RW knob and advance the film, the RW knob will rotate. If you're not
sure if the advance is working right I't an easy check to do.
Also if you've put you camera away & can't remember if there's film in it use the RW knob to check.
If there's tension, there's film in it.

 

[AgX]

I don't think I explained myself correctly. With time, the tension in the roll loosens up to the point of not, or barely, advancing if I pull the 'lever' after taking a photo. So, every time I take one, I have to turn the rewind knob clockwise, take a photo, and then advance the film, otherwise it's so loose that it doesn't move from its place.

I'm completely confused.