<human>: Can you summarize the given text in a few sentences?

I am freshly engaged and a relatively new graduate just starting my career. My fiancé and I recently started talking about combining our finances since starting my new job. (He's had a steady one for about 4 years making 40ish a year) I am very worried about combining our bank accounts. We originally were planning on just using my paycheck to pay everything and just put his into a savings account. Therefore, it would be a little tight for us for awhile until I hit my 6 month raise. This is a slight issue because we recently got a house and have some things we need to buy ahead of that. (None are urgent though) He expressed the idea of just getting a credit card and charging some of the things onto it. This frightens me for two reasons. 1) Before I met my fiance he was living paycheck to paycheck with 5k in debt from personal loans and credit cards that my grandmother helped bail him out of and 2) I feel like he doesn't understand how credit cards work. In the few financing courses I took in college my professors always said that the best thing to do was to use a credit card only if you could turn around the next day and pay it all off. That way you get the perks of having a card but don't get penalized on things like interest. 
My fiancé literally laughed when I told him this and said that as long as we make minimum payments and have about 20% of whatever we buy with the card in cash to go towards paying it, we shouldn't have to worry.  I just want to know who's right and if there are any suggestions or steps I should take in order to calm my nerves about us combining finances.
Sorry if this is confusing or doesn't make sense, it's late here and I'm close to getting hysterical.
<bot>: My non-finance savvy fiancé and I are thinking about combining finances. Any advice on best way to handle this and dealing with credit cards??