There are different types of information that is secured, with different uses for that information. Accordingly, there are differing methods available to protect data. To protect something like a database, one approach is to restrict access to that file using a password . Whoever holds the data may store a password for each person that requires access. In those cases, the data must be scrambled using a key - the scrambling changes readable plaintext to unrecognizable ciphertext .
Symmetric ciphers do just that.
Those algorithms encrypt data using a key, anyone wishing to read that data needs the same key. This method works great for keeping private data private, but suppose you wish to transmit the data to someone else. Managing a different key for everybody you wish to communicate privately with may or may not be a problem, but sharing those keys securely probably is. Asymmetric ciphers attempt to solve the key sharing problem by eliminating the need to communicate each key in secret.