It comes with easy-to-follow instructions. I did find that the molding process did not work super great (barely made any markings even if I bit down harder). I had to cut the bottom tray in the back a little bit because it was too big. I did like that it had little dots for tooth marks, so you could put little dots of the whitening gel on these areas. The syringe with the gel in it also makes it easy to make sure you are using the right amount.
I've used this a few times and am shocked my teeth have not been sensitive (which they usually are after using whitening products). The light was easy to use (though you do have to open the battery back and take out a film covering for it to work). It easily fit in my mouth against the trays. Pleased overall with these. Not a noticeable difference yet, but my teeth are not worse off. Will continue to use these until the gel is up. 3.5-4/5 stars thus far.
Want to check it out for yourself? Here is the Amazon product link:
*I received this product in exchange for my honest and unbiased review. Opinions are 100% my own*