Two ways, dial-up modems at home and wired ethernet at work/school.

At home you would use a Mac/PC/etc as a terminal, connected via telephone line to some host like Compuserve ou your workplace computer. This prevented use of the landline for voice communication, a source of some jokes.

At work your terminal/workstation would be connected 24x7 via wired ethernet, or some other LAN but ethernet became dominant in the 1980s, at first with coax cable.