"Going online" in the early days was different than it is now for most people.
Today, personal computers have Internet-connectivity software built into their operating systems (Windows or Mac OS or whatever). People basically rent a "data pipeline" from their phone or cable-TV company. The phone or cable company provides little or no content itself, but rather, access to content-providers' Web sites. From a software point of view, the connection works the same way regardless of the provider, because the protocols are standardized. You just hook up your DSL or cable modem, connect it to your computer with an Ethernet cable, and away you go.
In the early days, an online service provider like AOL or CompuServe had "access points" to its central server, that you had to "dial up" via an ordinary phone connection with a modem. You paid for the connection the same as any other phone call. If the access point was out of town (as it was for me) you had to pay by the minute for a long-distance phone call. On your computer, you used the provider's software, which could "talk" to only that provider's access points. You usually installed the software from a CD or a floppy disk. Each provider had its own e-mail system, forums, and collections of content.
In the beginning, different providers didn't connect to each other at all. If you were on CompuServe, you could send e-mail only to other CompuServe customers. Then they set up e-mail "gateways" to each other, and to the Internet when that started to become popular.