A lot of the currnet Shimano Spin Reels use a drag that has small (dime or penny) size fiber disks sandwiched between what are basically polished metal washers with a grease to keep the drag smooth (without pulling a reel apart I think there are three of each). Screw the tension nut down tighter and it puts pressure on this sandwich, which creates the drag. Pull the tension nut off (the top that holds the spool on), use needle nose pliers to remove the square retaining clip, then the drag disks will be visable. Easy to flick out with a toothpick. The fiber disks are saturated with a light reel grease (you can buy a small container at Fishermans at the Reel Desk for a couple of dollars that will last many years). This grease will disapate with use, moisture, hot days, etc. As the grease breaks down the drag will become jerky and feel very wrong. By re-greasing the fiber disks it will remedy this. I just use a toothpick to apply small amounts to several (4-6)places on each fiber disk,. Just make sure you dont over do it with the grease. If it is a new reel, this might not be issue but with some use you may run in to a similar issue and this is a good, easy, cheap fix. ( just make sure to pay attention to the order of the disks as you disassemble to be able to put it back together the right way).
