You can use PayPal on Steam by adding it as a payment method like you would a credit card. However, you'll need to be in an eligible country.
Bag yourself a Steam code worth up to $100 in this new PC hardware offer from MSI, which includes its gaming motherboards, ...
Your Steam Wallet is a digital-banking tool used by Steam to allow users to add funds to their Steam account, which can then be used in several ways.