First of all Your balance on your debit card is the same as the balance in your paypal account. Unless you connect it to a bank account to cover over withdraws you cannot spend more than what is in your paypal account.
to check your pay pal balance go to paypal site (www.paypal.com) choose account over view then acces account you willl be promted to enter your u/name then password and hey presto your in.
To answer your question on how to add balance in paypal please visit this support thread by paypal itself: CLICK HERE