At the end of any given month, you have things you have used or purchased, but have not paid for. These are listed as accounts payable. When you enter these bills into your computer system, your entry is a debit to the expense account and a credit to accounts payable.
Each month, you need to make a list of items that were in accounts payable at the end of the month. When you are closing out the month, you will have paid these bills, which were in accounts payable the previous month, reducing your cash. Using your list, identify the checks written for items that were listed in accounts payable the month before. You already listed the expenses the prior month - so you don't list them again.
The entry to show on your books that you have paid your accounts payable is a debit to accounts payable and a credit to cash. This reduces your cash and reduces your accounts payable. If you pay all your bills each month, this step will bring your accounts payable to zero (if not, the accounts payable balance in your books should equal all the outstanding bills).