How do you buy silver?

It depends on what type of silver you are looking for.

You need to have enough money to buy it. If you are looking for silver bullion or bars then you can go to websites that sell it, such as JM Bullion, but there are other sites out there as well.

If you are looking for elemental silver to do a project with your best bet would be to go to a website that sells chemical product such as Flinn Scientific. This website should be safe and secure as it is what professors and teachers use to order products. Again, there are other websites that exist, but those are just a couple different sources for you.