Then I suggest you study:
1) calculate the composition principle, understand what a computer is, what characteristics this device has, and what other devices are the same as it in principle.
2) Network principle, to understand how network devices communicate with each other. The key is to understand the protocols that guarantee network communication.
With these two points, you can further study in other aspects.
In addition, in practical work, the network administrator should not only manage the logical environment of the network, but also manage the physical devices in the network. Therefore, as a network administrator, you should also know about common network devices and their uses. Computer network can not be separated from computers, and computers can not be separated from applications, so the application of operating system is also the direction of learning.
In addition, as a senior computer network administrator, you must have some management knowledge.
To master the basic knowledge of computer network, Cisco's CCNA Reference Book is a good choice for reference only! You can find this series of books, one * * * four books, on several different topics of the network. Worth seeing!