1. 给…作注解（或评注）
If you annotate written work or a diagram, you add notes to it, especially in order to explain it.

1. provide interlinear explanations for words or phrases

e.g. He annotated on what his teacher had written

Synonym: glosscomment

2. add explanatory notes to or supply with critical comments

e.g. The scholar annotated the early edition of a famous novel

Synonym: footnote