Detecting a symbol in a user's input

I'm trying to make a simple (and useless) website for practice. It has a box for a user to type an entry. the user is supposed to add hashtags before an important word (and phrases, but the words should be together, no spaces). then i have a box after the entry box to show the hashtagged parts of the entry. what should i enter in javascript. This is what i need except in code: if user enters hashtag then take part that is hashtagged and copy into the output box. This is what my page looks like: My page