This is likely getting a bit deeper then introduction content but I know this one was requested so I'll tackle this one. There are lots of ways to know "for sure" but at the same time forgeries are also getting much much better as well.

Source-Also a great read with more details

First I'm going to say if it's too good to be true, it probably is and be cautious

Especially if your buying online somewhere or privately, or Ebay. They can fake just about anything, from modern numismatics like coins from the Royal Canadian Mint, to generic bullion or even collector coins and graded slabs. I've even seen forgeries of popular privately minted semi-numismatic rounds. Nothing is safe!

With that being said, if your new I would once again recommend sticking with reputable established dealers or very trusted sellers.

I'm going once again keep it more or the quick side, it's easily a full post on each method, and there's lots of great YouTube videos and resources available.

Look at them

This is very imprecise but you can usually tell a fake or at least feel a bit suspicious. Usually the finish isn't totally right and some minor details are missing or different. There are lots of books and guides that will walk you through some common forgeries. Again this comes with experience and it's not going to help you much starting out.

Precise Measurements

The method is just to weigh them and measure them. Everyone should have a good gram scale to take a quick measurement. 1 oz is 31.103 Grams and bad forgeries are usually way off. Even minted coins will have some minor variations, but a bad forgery will be way off. This is the same for the width and diameter. If you have yourself a good set of calipers you can often detect some differences. There is some variation in planchet diameter and thickness depending on the coin, but most are listed online to confirm. Measurement alone will not get you very far since most forgeries are much more sophisticated than this, but you'll pick up a few for sure.

Sound

If you have a good ear, you can always trust a "ping" test. I'm convinced I'm tone deaf and can't notice a repeatable difference, but it does matter just how you strike it. Pure silver is said to have a delectable "ping" sound when it's struck. Many people suggest striking it against a known genuine coin and listening. Like I said I for the life of me don't feel comfortable with this, but many people swear by it.

Magnetism

Silver is not magnetic, so this is another quick check and a poor forgery will often be magnetic and stick to a magnetic if it is just plated copper or other magnetic alloys. Beyond this is gets a bit technical but silver has dimagnetic properties, this is some real fancy physics stuff, but it does kind of react to a magnetic. This is pretty damn hard to see but people have made "coin slides" that can be used to test for fakes. It's not perfect either but another great tool.

Here's a video showing this I found on YouTube.

We'll take a break here and I'll once again suggest getting the tools above and check before you buy if your going to be buying privately at flea markets or local classifieds and such. Coin shows are usually much safer since those dealers usually have a reputation to uphold, but be leery of new vendors without an established reputation.

If you want to be really sure

I'd say those first few tests will do you pretty good spotting some fakes, but once again many are much more sophisticated than that. This is where you need to get into more advanced testing such as the ones below.

Acid test/destructive tests.

There are commercial acids that can be applied to coin surfaces to that will react a certain way with pure silver. Of course if it is plated and thick enough it will still react appropriately. So often when doing an acid test it's suggested to file down a portion or snipe or cut some. Of course these will destroy any premiums, but if you really need to know if it's real this will work. Just cutting it in half will also often reveal an obvious core of a different metal. You can also melt it, which will be apparent pretty quick,especially if your in the habit of melting silver, you'll be able to tell.

Specific Gravity

This one is based on another fancy physics principal regarding the density and atomic mass of pure silver. This one really works and can be pretty precise and doesn't need anything too fancy to complete. Essentially you weight a coin in air and also weight it suspended in water and do some math and compare. The video below explains it more and there are a lot of other online resources as well.

Electromagnetic Signature

This can be done very reliably by some fancy commercial machines that many big dealers or bullion stores have. If your LCS has one and your on good terms you can sometimes get them to scan them for you. There are household machines that cost around $800. The most popular one is a Sigma Brand Machine. I've watched a few videos of them in action and they are very quick and reliable, but of course also quite expensive. I'll post a video below with one in action.

This is a big one and like I said some more advance stuff, but there really are lots of fakes out there if you are not careful

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