How do you access the comments if you sent your paper in electronically? I'm assuming that you sent the paper in Microsoft Word. The comments should be apparent as soon as you open the paper (in the right margin, in balloons). I use Word's "Track Changes" feature, so that when I alter something in the paper there's a record in the right margin. I also put in comments, which appear there. If these don't appear, try clicking "Markup" in the "View" menu at the top of Word (it is a toggle switch, turning the markup features on or off), or "Comment", in the "Insert" menu, or try clicking "Track Changes", in the "Tools". The first of these options is the best. Make sure to scroll down - there may not be comments right at the beginning, but they may appear later.
If you sent your paper in WordPerfect, go to the "File" menu at the top. Under it, there's a tab called "Document", under which there's a button called "Review". Click that. It gives you the option of turning on reviewer's comments. Note that WordPerfect's reviewer's comments operate differently from Word's - they are inserted right in the text, and can be mistaken for text. Turning the button on will change the color of my comments, making them evident. In this particular case, Word's way of handling reviewing is superior to WordPerfect's, so I prefer to get papers in Word. (In other ways, by the way, I think WordPerfect is superior).
I use a lot of abbreviations for common problems when grading papers. If you see a number of the same comment on your paper, you should go over the entire paper to find other instances of the same problem that may not be marked. After awhile I don't note every example of a problem (e.g., there may be many grammatical errors, and after awhile I don't note them all). There comes a point at which the whole paper must be re-thought.