Teresa, there are 2 or 3 brass bolts that hold the tank to the lower bowl section of most toilets. These are pretty easily replaceable and the bolts have washers in the bowl to seal the heads of the bolts from leaking into the space between the two ceramic sections. You may as well replace the gasket that fits between the two sections while you are doing the bolts.
My suggestion would be to go to a plumbing wholesaler who will take the time to show you how to do this if you don't think that you can figure it out. If you remember that they have to take care of their regular and high volume customers first, most will be happy to tell you at least all that you need to know. The total cost for bolts, gasket and seal should be under $10. About the only tools you will need are an adjustible (Crescent) wrench and a big screwdriver. Don't forget to shut off the water to the toilet and then flush when starting the job.