How can I implement a full html,php,js and css page into a wordpress page?
Example:
I have a app.php that has a text box, when You press enter it displays the text with a php echo. With the users profile picture from Facebook.
How Can I inset/implement that into a WordPress page?
HTML/PHP: The simplest way may just be to create an extra template in your theme. You can view WordPress template hierarchy here: Template Hierarchy
JS/CSS: If the JavaScript and CSS makes the most sense to be embedded (it usually does!), you can use hooks and actions in a simple plugin (or potentially your functions.php page) to include the JavaScript and CSS you need.
Note: I have not personally used functions.php (found in your theme files) to call these sorts of hooks, but I assume it would work just fine.
If you are using a theme that constantly receives updates, it is worth building a plugin to do the job. If not, it’s easiest to just modify the theme.