Hi Tuong van,
"about 2-3 days" : About two to three days
We didn't talked (for) about two to three days
We started to talk about my schooling and his (schooling) back then, and how he came to learn a few words in Vietnamese, etc OK
Note that "schooling" is quite different from "school days". "Schooling" means "education at school" while "school days" means " the period of your life when you spend at school"
Best wishes