testimonials-grid-section-main

This is my first time using the grid. I struggled a litte bit to get the layout right. It would really be appreciated if you take the time to answer some the following qestion.

How can the container be centered ? Do I really need to use to subgrids for the layout or would suggest grid-area ? Do you see anything that can be improved ? Any tips on resources or ways that I use to improve my understanding of the grid ?