The official manual is dense. Many users supplement it with:

The manual guides users through a two-stage scientific processing workflow: GAMIT/GLOBK Tutorial | planetmechanic - Eric Lindsey

Alternatively, many users simply search for GAMIT_GLOBK_Manual.pdf via university repositories, but always ensure you have the latest version matching your installed code.

: Covers the Kalman filter processing used to combine daily GAMIT solutions into multi-year velocity fields and terrestrial reference frames. Key Workflow Steps Outlined in the Manual