How do you go about purchasing and using a Visa Gift Card for Online Shopping?

I've never used a credit card nor shopped online, but since a little money came in from my job I'd like to buy some stuff online. I already picked out a tablet case, keyboard, stylus, and wall charger on Amazon.can and have gotten all the way until the page where I have to include the code from the gift card.

I've yet to buy the card myself, I just wanted to see if I could get through the process on the website and so far it seems to be working. I plan on buying a $100 visa gift card and lucky for me the "total" price with taxes and shipping ended up coming up to $98. So I am good there

So all I need to do is buy the card, and this is where I have no clue. What do I say? What do I do? What's the process? What information do I gotta give? Do "I" have to go down and go through the process myself or can someone else do it for me under my name? I think once I get the card and its all set up, and I go back on Amazon's website and finish the process I will be good. Its just the process at the store that's confusing to me.

If you guys could help me out that would be great!