Hi,
An electronic device is not defined by a picture. There is a datasheet for every device.
There you find informations about pins, functions, wiring, interfaces, protocol and so on.
You need to read the complete datasheet thoroughly.
With this you need to decide how (with what interfaces and what signals) you need to connect the modem with your microcontroller.
Yes, the microcontroller is another part (we don't know) with datasheet that you need to read.
Usually the datasheets contain all informations you need to know to design your circuit.
But at the internet pages of the semiconductor manufacturers you will find additional informations, maybe even a wiring example.
There is no way around reading datasheets and application notes, every designer need to to this (boring) job, even the professionals.
Then start with the svhematic, either from the scratch or you modify an existing schematic.
If you are not sure, then show us your schematic, we will verify and comment it.
Klaus