There are many many different networking standards, each having been created for a specific set of conditions. Some have become very popular while others have remained in the niche for which they were created.
The most popular networking standard is Ethernet. The specifications for an Ethernet compliant device dictate which hardware and software must be used in order to make that device compatible with other Ethernet compliant devices.
The media access method used on all Ethernet compliant devices is known as CSMA/CD which is an acronym for Carrier Sense, Multiple Access with Collision Detection. In this approach all connected devices have access to the communication medium, the only rule is that the device may not send data if it can detect that another device is transmitting data.(this is the carrier sense part of the name). Once the "airways" are clear then any device can start a transmission. If two devices begin a transmission at exactly the same time then the connecting device(most often a hub or switch) will report a collision. Both of the transmitting devices will cease the sending of data, generate a random number and wait for the number of milliseconds to pass and then listen again to see if they can detect traffic. The device that generated the lowest random number will have to wait the shortest amount of time and get to transmit data first. Once the other device completes the wait it will detect the transmission of the first device and wait until the medium is quiet.
This approach leads to very efficient use of the available bandwidth but if the network is not carefully designed it can be very slow. This media access method is far more efficient when switching hubs are used with devices like bridges to reduce any unnecessary transmission of data.
CSMA/CD is not required on fully switched full duplex network because collisions are theoretically not possible, since each node would have its data sent only to where it is addressed and each node would only receive data that has been sent to it.
Token passing is another approach to access control, it is used as the media control method where the topology of the network is a ring or a bus. In Token passing there is an electronic "token" that is acquired by any node that needs to send data, only the node that has possession of the token may transmit and if a device needs to send data and the token is not available then it goes onto the waiting list.
In Token passing there can be no collisions but the waiting time on the waiting list can get quite long on a large and busy network.
There are many networking standards and many media access control methods within each networking standard, they all have certain advantages and disadvantages but we tend to use the most popular ones because the compatible hardware can be mass produced and can be purchased more cheaply.