Techopedia explains
Point-to-Point Protocol (PPP)
There are many physical mediums for point-to-point connectivity, such as simple serial cables, mobile phones and telephone lines.
For Ethernet networks, TCP and IP were introduced for data communication purposes. Both of these protocols have specifications for Ethernet networks only. Thus, TCP and IP do not support point-to-point connections. Therefore, PPP was introduced for point-to-point connectivity without Ethernet.
When two computers are being connected directly, both ends send a request for configuration. Once the computers are connected, PPP handles link control, data control and protocol encapsulation.