If you want to build credit, you have to carry debt and pay interest on it for at least one month. The second month of interest, through the rest of your life, does not accomplish anything productive. But your credit report shows the maximum past balance you have carried as one of three important numbers for the card, along with current balance and the current limit. If max balance carried is zero, it is as though you have never used the card, even if you use it every day. Your credit score will never go up due to the account, and it may actually go down if you have multiple unused accounts.
To build your credit, you need to build your credit limit. You do that by maxing out the card, while saving cash at the same time, pay one month's worth of interest, and then pay it off the next month. After your balance is back to zero, call the card company and ask for a higher limit. They will fall all over themselves to comply. If you make the same request for a maxed-out account, they won't give you anything. But by paying it off, you should be able to double your credit limit with each request.