Front End Post Form

Hello.

I’m tring to create a front and post form.

Code is here -> https://pastebin.com/g2zS5xDg

I want to add a controller, if title and content added and category selected, but taking this error message:

Warning: Cannot modify header information – headers already sent by (output started at /wp-content/themes/firma/firmaekle.php:10) in /wp-includes/pluggable.php on line 934

How can i do it? Any example code about it?

Thanks..