With umask you see the current mask, with umask -S you see it understandably. The default in Ubuntu is umask 022, which means that files will be -rw-r--r-- by default. With umask 026 you can prevent files from being readable and directories being accessible by "other"s (meaning anyone) by default (-rw-r-----).
You can also use the much easier symbols like with chmod, e.g. umask u=rwx.