I'm trying to create a new file within a folder in my rails application

I'm following along with the 'Rails Crash Course' book and it is telling me to create a file within a folder in a rails application that already exists.

I've searched the whole book but I can't find the instructions to create a file. I feel like this should be easy but I have searched online and cannot find a straight answer.

Here's an example: Create a new file named app/views/posts/index.html.erb and add the following code...

Here's another: Create the file app/views/text_posts/_text_post.html.erb and open for editing...

Anyone got the solution?