Write ~/count.sh. It takes two arguments, a word and a file, and writes how many lines of the file have the word:
text
learner@tidepool:~$ ./count.sh ERROR ~/logs/till.log
ERROR: 3Use $1 and $2. Make it run with ./count.sh.
Write the script
~/count.sh uses $1 and $2, has the shebang, and the owner can run it.