Each organisation is a place where your contacts work.
You can't make contact with an organisation itself (i.e. sending an email or sending an SMS) as this is usually just a building or an office block or school etc. However you can of course make contact with the people who work there. Those people are listed under the Contacts tab inside each organisation card.
Use the field Type to arrange your organisations into lists, e.g. secondary schools, employers, etc. This will make finding groups of organisations easier, and can be seen on the home dashboard in the ‘Organisations top 10 list’.
To see all of your organisations at a glance, arranged into an A-Z directory, simply click the Organisations tab.