“Everything is a file” describes one of the defining features of Unix.
grep
grep 'word' filename
grep 'word' file1 file2 file3
grep 'string1 string2' filename
cat otherfile | grep 'something'
command | grep 'something'
command option1 | grep 'data'
grep --color 'data' fileName
more about grep in How To Use grep Command In Linux / UNIX
How to View Logs Files?
less /var/log/messages
more -f /var/log/messages
cat /var/log/messages
tail -f /var/log/messages
grep -i error /var/log/messages
quoted from Linux Log Files Location And How Do I View Logs Files on Linux?
Piping Work in Linux
program1 arg arg | program2 arg arg
The vertical bar | is commonly referred to as a “pipe”. It is used to pipe one command into another. That is, it directs the output from the first command into the input for the second command. So your explanation is quite accurate.
more about | in