toilet repair (for complete novice)

Turn off the valve to the toilet and then flush the toilet, holding the flush handle on until most of the water is drained out of the tank. Then fiddle with the closing valve flapper and see how it settles onto the hole. You can probably make an adjustment to it to make it work better. It could probably use a little cleaning also, with a paper towel or whatever, and the hole it seats onto also.

Even if he replaces it, the hole it sits on should be cleaned and be sure not to drop anything into it by mistake or you will need a new toilet quite possibly.

As seen on Yahoo;

I don't think it was "wrong" Frankly I doubt if there is much use to using food dye to find out if it is leaking, after all the OP provided clear evidence that it is likely just that. I would tend to agree that it may well be better to buy a new flapper, making sure to get the right one for that toilet. As you noted they are not expensive and it is not worth my time. However the OP may find that he still needs to fiddle with it to get a good seal and he should carefully clean the seat.

If you've never done a thing to the toilet over the years, I'd go to Home Depot and get one of their Fluidmaster kits that contain everything you need to rebuild the whole innards. Kit contains new flush valve, flapper valve, gaskets, tank bolts and handle. While you're in there might as well do the whole show for about $17.00. Assuming you're tank bolts aren't rusted to death, the whole deal might take an hour.