php Form in steps (autosave after step 2)

You can do either using AJAX or php sessions.

Here is the AJAX way

function autosave() {

new Ajax.Request('autosave.php', 
{ 
    method: 'post',
    parameters: {id: $('id').value, save_text: $('myInput').value},
});

}

Now call this function with some Interval.

Other way is you need to place you code in php session and you need to habdle it like - every action you need to save your session data, sameway you need to load if you do back and forward.

Provide more details about php version, some forms, fields and database, I will edit my answer

Since you're new to PHP I'll give you an idea of what to look for. If your page doesn't use AJAX then validate the post data at each submission. If the post data is valid then save it into the session (use the $_SESSION superglobal) and save it to the database at whichever step you need and wipe out the data you just placed in the session.

Alternatively you can use AJAX and just submit the form when the required steps are completed.

Since you didn't provide any code I won't either, but I figure a nudge in the right direction wouldn't hurt. Come back and post another question when you have some code if you get stuck.