et and est are not realy homophone car their sound is quite different. However, it can be easy to make a confusion when writing them. So, again, you have to check their grammar function.
et is above all a coordination conjunction, that is to say it is used to do the link between the words and the ideas distinction: le chien et le chat.
est is a verb which comes from être. It can be found in conjugation: il est.
A first way to make the difference is to put the sentence to the past: est becomes était but et does not change.
A second way is to replace et by ou (or): le chien ou le chat. If the sentence has no meaning, it is sûrement est.