You launch your word processor and open the document. I need a good-size chunk of memory to hold it all. It asks the operating system if there's any memory available and, if so, can it have some. When you close the document, the word processor should release the memory back to the OS for use elsewhere. In short, the operating system itself provides very few services that are directly useful to you.
Most people log onto the Internet from their home computer by using a modem.
A modem is a circuit card, either in a box attached to your computer through a cable, or seated in a slot inside of your computer. The is the modulation phase. It converts those tones from the phone line into information your computer can understand. Just another computer wishing to connect to your network. I've got a spot open.