You can add personal Notes so that only you can see them. Click Notes then when you have typed whatever you want, tick the box "Make this a personal note?". If you have any comments that you think are of interest to other members, such as what worked or didn't work in a recipe, you can also add a general Note that will be shared.
You have a Notes tab on your Profile page (which you access from your username at top right) and you can there see all the Notes you have made in one place.