Well, there's always "man find".
To move around within a man-page first have a look at "man less" 
- next page: space bar
- prev. page: backspace
- search for stuff: /stuff
- next occurrence: n
- prev. occurrence: N
- exit: q
In case of the find command you've posted something like this would reveal what the "-o" means:
man find
/-o
now pres 'n' a couple of times
expr1 -o expr2
Or: expr2 is not evaluated if expr1 is true.
BTW: the '' is the 'line continuation' character. If you don't get any results for the search try the a simple search without OR and grep filter, that should work.
find / -iname "*rxtx*"
To filter out a filename you don't want, you can add another option:
find / -iname "*rxtx*" ! -iname "*download*"
or filter the end result of what 'find' produces through grep (which also prunes folders with that name):
find / -iname "*rxtx*" | grep -V -i "download"
If you're getting a lot of error messages and / or the results are zipping by, ignore the error messages by send STDERR to /dev/null and use 'less' to page the results.
find / -iname "*rxtx*" 2>/dev/null | less
A very good forum for linux questions is: www.linuxquestions.org
All sorts of documentation: www.tldp.org