i want to purchase bitcoins

If you're careful and do your own due diligence, you can use LocalBitcoins or Paxful. The main thing is to make sure the seller is verified and has a good reputation.

The exchanges like Coinbase and Virwox accept Paypal, but you need to verify your account and the fees are high.

Many sellers don't like using Paypal to sell bitcoins because the buyer can dispute the charge (if using goods/services) or do a chargeback. I've read many stories about people receiving money from Paypal and then the buyer disputing the charge. As it's an untraceable, digital good, you cannot prove that it was delivered so you always end up losing the case as the seller.