Here are the first part of the instructions.
Nest the existing input element inside a form element
This is the existing input.
<input type="text" placeholder="cat photo URL">
You need to use that one.
Do not create any more inputs.
Do not alter that input.
Wrap your form tags around that input.
<form>
EXISTING INPUT GOES HERE
</form>
Here are the last part of the instructions
assign "https://www.freecatphotoapp.com/submit-cat-photo" to the action attribute of the form element.
You need to use that url I just showed you in the action attribute.
Here is the complete structure for the code.
<form action="URL I SHOWED YOU GOES HERE">
EXISTING INPUT GOES HERE
</form>
If you are successful, then you should only be adding two lines of code.
One line of code above the existing input.
One line of code below the existing input.
If you are adding more lines than that or changing the existing input then you are doing it wrong.