Questions & Answers about Он слегка открыл дверь.
Открыть is the infinitive, meaning to open.
In the sentence, we need a finite verb, not the dictionary form, because the action actually happened.
- открыть = to open
- открыл = opened (past tense, masculine singular)
So Он слегка открыл дверь means He slightly opened the door / He opened the door a little.
Он means he.
Russian often allows the subject pronoun to be omitted if it is clear from context, so in some situations you could also just say:
- Слегка открыл дверь.
But using он makes the subject explicit. It can help with clarity, contrast, or emphasis.