A head gasket is basically a shim which can compress slightly, so that a seal is formed when the cylinder-head is torqued down onto the cylinder block. Unless both the block-face and the cylinder head face are perfectly flat you will always need a head gasket to take-up and slight machining differences between the two. They are not subject to wear and tear, since there are no moving parts to cause them to leak, however if your car has, at some time, run with very little coolant, or has frozen-up, both of these can cause the head gasket to fail, since the engine block and the cylinder head can, under these kind of circumstances, expand/contract at different rates causing warpage, and if the difference is big enough the gasket seal can fail.
A compression test on each of the cylinders may point to where the problem lies, also, as has been said, you may well see white crud (oil/water emulsion) forming on the oil filler cap, caused by coolant from the cooling system finding it's way through the failed head gasket into the oil circulation system.
If you are not mechanically-minded, and it would seem so, probably your best bet would be to find a local small garage who can advise you.