This is the 3727th most frequent Russian word.
учебному
"Учебному" means "educational" or "related to learning/study" in the dative case.
Here, "учебному" is the dative case singular adjective form of "учебный," modifying "пособие" (guide) to describe it as educational.
Этот материал относится к учебному пособию.
This material relates to the educational guide.
In this sentence, "учебному" is used in the dative case singular to describe "процесс" (process), indicating that it is related to learning or education.
Я верю в его подход к учебному процессу.
I believe in his approach to the educational process.
Here, "учебному" describes "план" (plan, i.e., curriculum) indicating that it is associated with education, in the dative case for grammatical compatibility.