I bought a prepaid Bell card for my cell phone....?

[♪♫Two Of Us♫♪]

I bought a prepaid Bell card for my cell phone so I can have minutes this month. I briefly read the back side of it to see how you get the minutes (25 dollars worth). When I got home, my mom lost it and now I can't remember what it said. How do I put the $25 onto my cell phone? I have the PIN number, I just don't know how to.
Thank you in advance!!!!!