Polednikova asked about this in the Halloween thread. It is pretty tricky to the native english speaker. I have troubles with it too. It seems to have different roles, accordinig to the placement in the sentence. When at the beginning it seems to be simply introducing a subject. Could be singular, plural, feminine, masculne,... we just don't know until the subject is defined. The first clue comes with the form of verb To je...it is to jsou...they, those are Can even be....To jsem já..It is me.(literally I think 'I am it'. Another role is to declare the pronoun 'it' in a sentence. This is still perplexing to me and I often get it wrong. Sometimes the 'to' is needed and sometimes not.