These are simply two ways, one temporary, one permanent, in which the computer stores information. Apple Macintosh computers require less memory and disk space to perform the same functions as their PC counterparts, but most come with 64MB of Ram and a 6GB hard disk as standard. Many PCs and Apple Macintosh computers come with modems built in. You simply plug one end of a lead into your phone socket and the other into the back of the computer. If the modem isn't included with your computer you have to buy a separate unit.
Modems vary in the speed with which they can transmit data between computer and internet.
Finally, whatever computer you have, using the internet will involve looking at the screen for long periods, so make sure you buy one you are comfortable with. If you are buying by mail order, find out what screen will be supplied and go and take a look at it in a shop. The sharper the screen, the more it will cost, but the better for your eyes it will be. There are about 1,000 ISPs in the UK at the moment. Many provide you with the facility to create web pages of your own.