Most stores such as Walmart use a machine that turns your check into an electronic funds transfer and will pull the money directly from your checking account once they put the check through the machine which they do immediately.
If the funds aren't in the checking account then the transaction won't complete and you won't be able to make the purchase and have to put the stuff you're buying with the check back.
If the store doesn't use a machine to automatically pull the money out then once your check gets to the stores bank or the persons bank then your check will be returned to the person or store as a insufficient and the store or person can be charged a fee for returned check which will then be passed onto you and you'll also have an overdraft charge.
If you overdraft too much then you'll have your checking account closed and a mark put on chexsystems which will prevent you from opening another checking account for at least 7 years.
Always make sure you have enough money in your checking account before writing a check.