List Builder with multiple input fields

Hi there!

About myself: I am pretty new to web developement and i would set my skills just a little above beginner.

Now i ran into a problem. I want to create a "List Builder" with more than one "input" fields but just one "output" field, or at least make categories(unselectable for visibility reasons) inside one input field. I tried the XMultiselect extensions but it doesnt fit my exact needings.

The reason why i want it this way is because i want to create some form of "Playlist" with multiple categories.

Maybe i try a very wrong approach anyways, if so please push me a little into the right direction.

Please help a newbie …

PS: I would link to that extension but its not allowed in the first post

if you found the solution, tell me too. thanks