need SIMPLE grep piping examples

[Thiers Botelho]

After doing my usual googling and browsing for the right way of doing 
things, I finally gave up on this one.  :(

Seems that all documents with examples for **grep** are filled with 
explanations on regular expressions and advanced usages. Even _man_ and 
_info_ don't show SIMPLE and BASIC examples, and even with trial 'n error 
I couldn't figure out the right syntax and delimiters.

Would anyone point me to some very basic but extensive page on grep usage 
? 

All I need to do right now is something like:

df -m | grep [ 'ilesystem' , '/dev/foobar' ]

(I need to show any line containing _either_ of the strings)

so that a script could output just the header line of 'df' plus the single 
line describing '/dev/foobar' below it.

Thnx . . .

Thiers