Shortcoder is a plugin which allows to create a custom shortcode and store HTML, Javascript and other snippets in it. So if that shortcode is used in any post or pages, then the code stored in the shortcode get executed in that place.
What you create in Shortcoder
In shortcoder administration page, you create the following.
Shortcode name:
subscribe_form
Shortcode content:
<form method="post">
<input type="text" name="email-id" placeholder="Enter email to subscribe" />
<input type="submit" name="Subscribe" />
</form>
What you insert in post
In post admin page, you insert the below shortcode to get the above subscribe form.
[sc name="subscribe_form"]
What you get as output in the post
Once you save the post and open it the shortcode is executed and you get the shortcode executed in the content. You can create as many shortcodes like this as per your requirements