It is slightly different, but no biggy.
I assume you already know how to load 35mm so let me just focus on the differences for 120 film.
The main diff is that 120 film comes with a backing paper. This paper will have to be detached from the film. The film is also wider than 35mm so your developing spiral spool will have to snap out to the wider width, which can be as simple as turning the two wheels in opposite directions and snapping them back. Check the instructions on the spiral.
The removal of the backing paper is easy. The film is attached to the backing paper by means of piece of very short paper tape at the beginning of the the roll. When you unroll an exposed roll, you will actually encounter the tail end of the roll, which is not taped onto the backing paper. You can start loading that end onto the spiral first and when you reached the beginning of the film, that's when you meet the tape sticker. Simply remove the sticker from the film or the backing paper to detached them. Continue rolling the remaing part of the film until the entire strip of film is within the the spiral.
The rest of the steps will be similar to the 35mm film. Note that you are likely to need more developer solution to make sure the entire roll is submerged.
For more details, I recommend you look for a book on this subject, the many good sites on the internet dealing with this subject.