Today you saw that you must use a valid DB2 username when using and installing DB2. The username must be fewer than 20 characters long or have the Act as Part of the Operating System advanced user right.
The three different installation types are Custom, Compact, and Typical. Normally, you would use the Typical install type, but you should understand what the options are to ensure that this install type is right for you.
DB2 requires a username and password to be specified for the Administration Server.