"This is my mother."
Translation:To jest moja matka.
You would only say this if you despise your mother. "To (jest) moja matka." uses construction to (jest)/to (są) + nominative and sounds quite normal. "To jest moją matką." uses "to" as neuter demonstrative pronoun with implied omitted noun and suggests that you don't consider your mother a human - you can't omit "jest" in this sentence. "To jest moją mamą" is very strange, on one hand you are expressing hatred by using neuter pronoun, on the other love by using diminutive. "Ta jest moją matką" uses feminine demonstrative pronoun, and as unnatural and pompous as it sounds, could be used in poetry or theatre play. "Ta jest moja matka." sounds biblical, in modern language is not used at all. Don't mix them!