Learn Russian: Врач быстро идёт по коридору. - The doctor is walking quickly along the corridor.

The preposition по means along or down in this sentence, and it requires the Dative case. For a masculine noun ending in a consonant like коридор, you form the Dative case by adding -у.

Why is the verb идёт used instead of ходит?

The verb идёт is a one-way (unidirectional) verb of motion. We use it here because the doctor is currently walking in one continuous direction down the hallway. If the doctor were pacing back and forth or walking around the hospital generally, we would use the multi-directional verb ходит.

How should I pronounce по коридору?

In Russian, short prepositions like по attach to the next word when you speak. Because the stress in коридору is on the third syllable, the о in по is unstressed and reduces to an 'ah' sound. You pronounce the phrase together as one continuous block without a pause.

Could I put быстро at the end of the sentence?

Yes, you could say Врач идёт по коридору быстро. Russian word order is flexible, but putting the adverb быстро before the verb is the standard, neutral way to describe an action. Moving it to the very end would place a heavier, special emphasis on the speed.