Two shared google files are provided. One is for general remarks (if any) on the analysis and/or publication strategy, and on the title and abstract. The other is for the line-by-line comments. The fields in the tables to fill are self-explanatory. You do not need to fill in the right order, the spreadsheet could be (hopefully, never tried) sorted later. Remember that comments should be classified as type A (style, typos and the like) or B (clearness of the discussion, real or apparent flaws or inconsistencies in the analysis, or in the description of the analysis, ...).
Please suggest modifications, if you feel they are needed, but refrain from just saying "this should be modified". The latter attitude is of no help to the authors (and in general irritating)
Check publication guidelines if you are unsure on whether a comment is applicable (the guidelines are very instructive)