Web of Science provides access to the Science Citation Index Expanded (1945-), Social Sciences Citation Index (1956-), and Arts & Humanities Citation Index (1975-). The fundamental question which can be answered quickly by Web of Science is where and by whom has a particular paper been cited. A list of journals covered is available from the publishers web page.
Short tutorials and recorded training sessions are available on a number of Web of Science search features, including creating citation reports, from the ISI training website.