There is no ``print file'' option (as far as I know) which sents the output of the MAGMA session to a printer attached to the computer. To do that, you must log the session using SetLogFile and then print out that file using some other program. There is a PrintFile command which prints the output to a file.
To have MAGMA print out a string or some variable values to the screen, use the print command. For example,
> a:=3; > b:=5; > print "a is equal to ",a,"\n","b equals ",b; a is equal to 3 b equals 5
Note the \n is the newline character.