I just downloaded the latest Ubuntu, it is a reasonable download ~700Mb. Before I burn it to disk it is a good practice to verify the copy by checking the SHASUM.
Usually the publisher of a file supplies the sum when it is released. In my case it was in the ftp download directory.
In the past I have been using MD5 sums to check the files, but there have been talk the possibility of these being hacked. SHA sums are much more complex than MD5’s as shown below.
The usage of MD5SUM is very simple as shown in the help text. This is exactly the same for SHA256SUM.