Quote Originally Posted by sperk
1. Мы решили остановиться у первого же дома, где увидим свет в окнах.

why is увидим in the present when the sentence takes place in the past?
It is not the present, it is the future. Perfective verbs don't have the present tense because what happens in the present time, is not completed. The order of tenses is different in Russian than in English (and much simpler too). To the moment that they decided to stop, the action "when we see the light" is still in the future.
2. Обычно он мог ответить на вопросы преподавателя, но молчал.
3. Я вижу, что иногда он хочет помочь нам, но не решается предложить свою помощь

Why is the perf. (ответить & помочь) used for thеsе sentences? It seems like it's a repetitive situation with (Обычно & иногда) not a one time thing.
These both constructions are imperfective verb+perfective infinitive (мог ответить, хочет помочь, не решается предложить)
The repetition is shown by the first part, and the perfective infinitive shows that is is one completed action every time.

If you use imperfective infinitive, like
мог отвечать
it will be like a continuous tense in English:
could be answering