If you are unsure which database to choose, help is at hand online. Some major hosts provide the facility for comparison of the number of occurrences of input search terms within each database they hold. However, it is advisable to ascertain names of the major databases in your area before you commit yourself to accessing a particular host which may not provide those particular databases.
You access a particular host computer via your terminal/PC by means of national and international data networks and once linked to your host you can call up the database you require.
For example STN - the Scientific & Technical Network carries many databases in the fields of chemistry and chemical engineering. STN is widely used in European universities, many of whom make use of the special academic password which can be supplied to educational institutions.