Edit: How come post about a partition I did in 3 days outperforms a post about bathroom remodel I worked at for 2 months, lol.
The door, frame, and handle are usually sold separately. You can grab them at any regular hardware store.
Leave a 10 mm gap all around between the rough opening and the door frame, then adjust it plumb and level using a drill and a long bubble level - or ideally a laser if you've got one.
Anyone can do it if they just know how, and YouTube is full of solid tutorials.