Error message while updating ubuntu 18.04 using terminal

I get the following error messages:

N: Ignoring file 'openboard-xenial.list.save.1' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
E: Type 'sudo' is not known on line 2 in source list /etc/apt/sources.list.d/openboard-xenial.list
E: The list of sources could not be read.

List files like openboard-xenial.list have a specific structure. Other than comments or empty lines, every line needs to start with either deb (for a repository with binary packages) or deb-src (for a repository with source code packages). In your case, line 2 of /etc/apt/sources.list.d/openboard-xenial.list starts with sudo for some reason. You need to look into that and correct it.

The other message is a notice that there is a file that is ignored by apt, because it doesn't have the proper file name ending. List files need to have a file name ending with .list, like your openboard-xenial.list. The file openboard-xenial.list.save.1 has a different ending and is therefore ignored. It may be a backup copy created by some text editor you used to edit your files.

The latter message is only a notice (N), compared to an actual error (E) like the message about the unknown type sudo.