Creating a form where users can edit their own submissions I'm beginning with Drupal. I've got to set up a multistep form which allows users to add content. I want them to be able to edit their own submissions too.

I began to code a custom module in drupal/php but I'm not sure it's the easiest way. I've heard a lot about Drupal native forms or content types that could do it as well as a custom module.

My question is : what kind of modules do I need to build a multistep form with own submissions edition ?
In the 
Home » Administration » Structure
and in the content type
add new content type and create your forms as you need 

You can edit every content type i.e. node and 
for editing own submissions you can set appropriate permissions like 'edit own content' in the 
Home » Administration » People  under permissions tab

For multistep forms
you can in the hook_form_alter() create 

$form['redirect'] = 'your_next_form_path';

By using redirect as soon as the form is submitted you will be redirected to other form (only thing is proper path for node or form needs to be mentioned).