Users can create/edit comments in Cinchy by selecting Comment from the context menu or hovering on a cell with comments.
Generally you should delete a comment only when it does not make sense (ex. you misclicked and commented on the wrong cell). If the issue brought up in the comment has been resolved, generally it is recommended to simply archive that comment.
Users who can view the cell can view and create comments on a cell. You can edit, delete or archive your own comments.
Users who can modify approved data (non-Maker/Checker table: edit permission, Maker/Checker table: approve permission) can also archive comments. For convenience there is also an Archive All button at the top that can be used to archive all the comments on that cell.
Comments are stored in the [Cinchy].[Comments] table, you can see the structure below.