Listing, setting and changing standard ugo/rwx permissions in numeric and symbolic form

Every file and directory has an owner user, an owning group and three sets of permissions: for the user who owns it (u), for members of the owning group (g) and for everyone else, the others (o). Each set has read (r), write (w) and execute (x). ls -l shows them as ten characters, for example -rwxr-x---: the first character is the type (- file, d directory, l link), then three characters each for u, g and o.