An ISP (Internet Service Provider) is a company that collects a monthly or yearly fee in exchange for providing the subscriber with Internet access.
An ISP might provide dial-up service, cable, DSL, or other types of Internet access. Some ISPs are local while others are national. A national ISP will provide access throughout most of the nation, while a local ISP will only serve subscribers in a limited geographical region.
When looking for an ISP the initial consideration is the type of access desired. Some ISPs only offer dial-up access which is the slowest type of connection. If you want cable service, you'll be checking with your local cable TV provider to see if cable access is offered. For DSL service, you may have multiple choices - or it could be that DSL is not yet available in your area. Often this can be remedied with a call to the phone company to upgrade local telephone lines.
The Terms of Service contract of the ISP will also state rules about hacking, protecting copyrighted materials, denial of service attacks, harassing other people, spam, compromising the service, and many other issues. These are as much for the legal protection of the ISP as to let potential subscribers know what the ISP will and will not tolerate. If you are planning on using web space provided by the ISP, check for limitations here too. Many ISPs do not allow commercial websites to be set up on their servers. This usually means that nothing can be sold from your personal webspace, including for example, a software program you wrote, original music, or any other item. ISP websites are normally for personal use only, to blog, post pictures, and so on.