Answer:
Silver certificates were issued for almost a century in many designs and denominations so that's far too broad a question to be answered without writing a small book.
Many late-date (e.g. 1957) $1 silver certificates are worth only slightly more than face value because they were saved by the carload when the government announced they would no longer be printed. However, older silver certificates and those with higher denominations can often be worth a premium. If you have specific bills, please post a new, separate question or check one of the links below. If you have an older bill, include its date, denomination, and what letter if any is below or next to the date (e.g. 1935 G). You do not have to copy the bill's serial number.