Buy Physical Metal
Purchase physical silver. There are a wide variety of investment grade (fine) silver bullion ranging from one ounce rounds minted by national governments, such as U.S. Eagles, Canadian Maples and UK Britannias, to 100 and even 1,000 bars produced by private minting and mining companies. These are available from local shops, online auctions and through mail order from bullion dealers. Because of the relatively low price of silver, a considerable investment (say $25,000) can purchase several tons of the metal, so it's unlikely large or even moderate investors will own their entire precious metals allocation in physical silver. But having at least some on hand can provide peace of mind in the worst of financial and economic calamities.
Speculate with the ETF
Even though silver bullion is fairly easy to liquidate, buying physical metal is generally a long term investment. Many investors, cognizant of silver's volatility and unwilling to take on and store large quantities of metal, prefer to speculate on more short term price movements. The most common and convenient way to do this is through the iShares Silver Trust exchange traded fund (ETF), which trades under the ticker symbol SLV. The fund can be traded like a stock, but tracks the price of silver with reasonable reliability. It is not redeemable in silver (except in very large quantities) and over time tends to lose value relative to actual metal. But, for short term speculation there is no more convenient investment vehicle.
A more traditional way to speculate on the price of silver is through the stock of mining companies. This is still a favored method for many savvy investors, but is fraught with risk. Mining is an inherently risky and expensive enterprise and individual mining companies are subject to a variety of factors independent from the price of the metals they produce. Nevertheless, stocks of silver mining companies generally react positively to increases in the price of silver. With some research, you can identify the well-positioned mining companies, but it's also possible to invest in a variety of miners through a variety of ETF or mutual fund products.
Participating directly in the silver futures market is reserved for the most advanced traders. Futures contracts expire each month, which can force a trader to sell at a loss to avoid taking delivery of actual silver. The contracts are large and expensive, so most futures traders use margin accounts, which is another source of risk. When done properly, speculating on silver futures is a direct and precise way to gain exposure to the price of silver, but, by its nature, is a relatively short term investment.