Questions & Answers about Я встал и пошёл к окну.
Because Russian past tense verbs agree with the speaker’s gender in the singular.
- встал, пошёл = masculine speaker
- встала, пошла = feminine speaker
- встало, пошло = neuter
- встали, пошли = plural
So this sentence tells you that the speaker is being presented as male, or at least grammatically masculine.
Встал is the past tense of встать, a perfective verb. In this sentence it means got up or stood up.
That is important because English stood can describe a state, but Russian встал describes the action of rising to one’s feet.
Compare:
- встал = got up, stood up
- стоял = was standing
So Я встал is not I was standing, but I got up / I stood up.