Well, no, not necessarily. You buy the card (lets just say it's a normal VISA gift card. Something you'd get on Christmas) You'd have to activate it, which, if you bought it from walmart and it came in one of those little sleeves, you'd go to this website and activate your card by following the instructions. Then, it's activated. (That only works I think if it comes in the sleeve thing from wm).
Otherwise, if it's just a normal VISA gift card, then yeah, you'd follow it's activation instructions and if it doesn't have any then I'd just add it to paypal and wait for your balance to update. If that doesn't work i'd troubleshoot accordingly.
(Sorry if this is a bit confusing i'm bad at explaining things rip)