The first thing you need to do is identify the glcd as there are many different 128x64 glcds and
they can use different controllers. Even when the same controller is used on different manufactures
128x64 glcds, the pinout can be different.
If (reference to company selling counterfeit product removed by moderator) provided a datasheet,
that will indicate the controller used on the glcd.
But there are many cases where the datasheet provided or supplied by low cost sellers is incorrect
so make sure to verify that the data sheet you have is for the glcd you have.
If you look on the back of the glcd you will see a part number like 12864J, QY-12864F, LM12864LDW, etc...
You should see this same part number in the data sheet.
If they don't match, then you will need to locate the proper data sheet.
Once you identify the glcd and have the datasheet, you must then identify the controller used.
It will normally be mentioned in the datasheet and will be something like ks0108, ST7920, etc...
Once you identify the controller used, you can then search for a library to support it.
Two popular libraries are:
Once you find a library that works with the controller on your glcd, you then must
use the libraries documentation along with the pinout on the data sheet to wire it up.
After that, the library will have example sketches and API documentation for how to
"talk" to the glcd to make it "do things".