Storing input data PHP

Im new to coding and im trying my hand at making a simple blog. i simply want to store and retrieve user data thats been entered. i understand that in HTML i cant just save the information as a document and needs to use PHP for data storage.
i think i have the right idea but i may be wrong.

Today's Activities


  <label for="date">Todays Date</label>
  <input type="date" value="label" name="date" id="date">

<br>
<!---Activities--->
  <label for="userinput">What Happened Today</label>
  <br>
  <textarea name="userinput" cols="50" rows="15" id="userinput"></textarea>
  <br>
  <input type="submit" value="submit">
  
</form>

i also have a 2nd file called process-form.php with the code

<?php print_r($_POST); ?>

when i submit data i get redirected to a paige with
"<?php

print_r($_POST);
?>"
instead of the data entered. am i was off or am i in the right directio?

If you just need the input that has just been entered by a user, you can get the value with Javascript:

const userinputField = document.getElementById('userinput');
const submitButton = document.querySelector('input');
const getValue = () => {
	console.log(`Do something with ${userinputField.value}`)
}
document.addEventListener('click', getValue);

Once the browser gets reloaded, the input is gone, though.

If you need that data for sending an email, for example, getting redirected to a PHP page should do, indeed. In the PHP file, you should be able to access the data like:

if(isset($_POST['userinput'])) {
  /* do sth with the data */
}

If you really need to store the user input for longer than the browser session, you need a database. That is often built with MySQL. And you need an API, that has access to the database and retrieves the values. That is often done with PHP and MySQL. Then you need a frontend application that retrieves the data from the API. That is mostly done with HTML, CSS and Javascript.
The full stack path teaches you how to build an API with Javascript (Express). So at the end of that path you might be able to build such an application.