Certificates are financial products that reflect the performance of company sets (indexes) or commodities (gold, silver, platinum, etc.) In other words, you can buy Certificates of a sectoral index (such as banking or telecomunications), of a commodities (gold, platinum, etc.) or of a regional index (such as STOXX 50, S&P500 or PSI20).
When you invest on Certificates, you are investing on all the companies that compose an index or on commodities, without having to buy it. Imagine you buy a S&P500 Certificate. When you buy this Certificate, you are buying a part of each one of the 500 companies that compose the index. So, if the value of S&P500 rises, so will your investment.