In music notation, sforzando is abbreviated "sfz" or "sf" and is used like other loudness markings. It indicates that the music after that point should be played suddenly and strongly forte. The word means "forcefully" in Italian.
When added to the staff, it looks something like this (complete with eigth notes and an initial mezzoforte marking):
/\
---| /----------------------------------------------------
|/
---/---------------*---------*---------*---------*--------
/| | | | |
-/-|/\--------*---|-----*---|-----*---|-----*---|---------
| | | | | | | | | | |
|--|--|------|----|----|----|----|----|----|----|---------
\ | | |____|____|____|____|____|____|____|
--\|_/----------------------------------------------------
|
\| mf sfz