if (when appended to a dictionary-form verb and followed by a present-tense sentence)
Benkyō suru to wakaru.
If you study, you'll understand.
Endaka ga susumu to, nihon keizai ga konran suru.
If the high yen continues, the Japanese economy will be in dire straits.
Ni to san o kakeru to roku ni naru.
If you multiply two and three, they make six.
when (when appended to a dictionary form verb and followed by a past-tense sentence)
Manhattan e iku to, daigaku no tomodachi ni atta.
When I went to Manhattan, I met a friend from university.
と(to) in the sense of "and" can only be used to conjoin nouns; not verbs or sentences. They are joined by conjugation.
と(to) in the sense of "and" implies that the list is complete. In the above sentence, the subject only speaks English and French. To imply other items, the particles とか(toka) or や(ya) are used in lieu of と(to). The particle など(nado, “etc., and so on”) can be appended to a list of nouns conjoined by と to imply that there are other items on the list.
と(to) in the sense of "if" can be interchangeable with the conditional particles ば(ba) and たら(tara)/なら(nara) if the conditionals describe a hypothetical effect of an action.
When と(to) is used in the meaning "when" it implies that something happened abruptly. See とき(toki).