How can I write a script that displays the words "I should have studied" to stdou when run?

If you're typing directly at a shell you can

echo "I should have studied"

To create a script, all you do is put the commands you want to be run into a (text) file and use that file:

Using you preferred UNIX/Linux editor, create the file study. You can use any name you like (including one with a .sh suffix if you prefer). Add these two lines to it

#!/bin/bash
echo "I should have studied"

The first line declares that it's a bash shell script. You don't need to filter the output with grep as the echo command does enough all by itself. (Also notice you don't type the leading $; some people use this on StackExchange and other sites to show they're typing a command but personally I think it's confusing.) Now make the file executable so it can run like any other program on the system

chmod +x study

And run it

./study

The leading ./ tells the shell to look for the command in the current directory. If the script was in a system directory or otherwise in your search path ($PATH) you would be able just to type its name, study to run it - just like any other command.

For syntax checking, don't be afraid to use https://shellcheck.net/ as and when your scripts start to develop.