There are many different ways to draw diagrams, and that is just within a single type. You can draw diagrams that depict logical topology, which can differ from the physical topology. Some people use the Cisco stencils, others prefer colorless boxes, others use lines to depict entire VLANs.
Sometimes reading a diagram is a lot like deciphering a foreign language, which is why I said practice is the best method.
That's not a network diagram.... That's a flow chart someone wanted to call a network diagram.
In order to "read" one, you have to know what it's showing.
Is it high-level? Is it low-level? Is it physical? Is it logical? Is it just a part of the network (service/application)?
After you answer that, then it's just a matter of deciphering where things go. Just like a map of a city, you can either have too much or too little information depending on what you are looking for.
You have to know what you are looking at/for before knowing how to read each particular map/diagram!
Network diagrams or any other type of illustrations are just a graphical representation of information and knowledge.
So if you have difficulties reading network diagrams, this means you need to learn basic networking elements like :
- - type of devices (Router/switch/FW...)
- - IP addresses, masks, subnetting, VLANs
- - Type of connections and interfaces.
- - ...
I recommend you just to be patient and learn things step by step, it is far more efficient.
Finding that "VRF" is "Virtual Routing and Forwarding" or that "PVLAN" is "Private Virtual LAN" will not help you if you don't understant the concept behind.
It is like reading programming language by using an english dictionary.
The point is not to read but to understand.