Когда я вижу их у входа в театр, я говорю «Здравствуйте».

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Breakdown of Когда я вижу их у входа в театр, я говорю «Здравствуйте».

• в: to
• говорить: to say
• здравствуйте: hello

Questions & Answers about Когда я вижу их у входа в театр, я говорю «Здравствуйте».

Why is когда used here? Does it mean when or whenever?

Here когда literally means when, but in this kind of sentence it often has the sense of whenever.

So:

• Когда я вижу их у входа в театр, я говорю …
  = When / Whenever I see them at the entrance to the theater, I say …

Because both verbs are in the present tense, the sentence describes a repeated or habitual situation, not just one single event.

Why is вижу in the present tense?

Russian often uses the present tense to describe a habit or repeated action, just like English can:

• When I see them, I say hello.

So я вижу here means I see in a general, repeated sense.

Also, вижу is from the imperfective verb видеть, which is the normal choice for ongoing, repeated, or habitual seeing.

Why is it вижу, not увижу?

Because увидеть / увижу is perfective, and perfective verbs usually refer to a single completed event in the future.

Compare:

• Когда я вижу их... = whenever I see them / when I am in the habit of seeing them
• Когда я увижу их... = when I see them one day / when I do see them in the future

In your sentence, the meaning is habitual, so вижу is the natural choice.