If this command worked, you should find two new files, called integral.log and integral.dvi, in the same directory. The file integral.dvi contains the formated text in a binary format. If you have a modern Unix with KDE, you should have a program called kdvi to view and print this file, finally revealing the integral in all of its glory. If you don't have this, you should have xdvi for viewing and several programs for converting dvi-files to various printer languages. The most interesting one of those is dvips to convert from dvi to postscript.
Some commands have an effect on the next thing.
If that next thing should consist of more than one character, these characters have to be grouped. Also, most commands appearing within a group lose their effect at the end of the group. Commands consisting of letters end with the first non-letter. If that non-letter is a space, the space is not introduced into the text. Commands can also consist of a backslash followed by a single non-letter.