<human>: Can you give me the gist of the text in a nutshell?

As a recent graduate (female, 22), I have really enjoyed going through the posts in this subreddit; it has really helped me beef up my budget and think long-term.  However, I got married in June, and my husband has a credit card from Bank of America, where he was given a year with no interest.  Naturally, it was maxed out when we got together.  So, I am close to paying it off, but his last billing cycle without interest ends December 8.  So, I don't understand when interest will apply (say for example, I can pay it completely but a few days after the 8th - will I still get hit with interest?).  Also, after that when and how does interest get applied.  Basically, I'm looking for a stripped-down (explain to me like I'm five-type) explanation of how to use a credit card without paying any interest at all.
<bot>: Got married; husband will have a bit of balance on card when his 1-year, no interest runs out; how do I use credit card without paying interest