<>To have the difference, put the sentence to the first person. Then, s'est becomes me suis but c'est stays the same.
C'est un garçon. => C'est un garçon.
Il s'est levé de bonne heure. => Je me suis levé de bonne heure.It is also possible to put a negative form. C'est becomes ce n'est pas and s'est becomes ne s'est pas:
C'est un garçon. => Ce n'est pas un garçon.
Il s'est levé de bonne heure. => Il ne s'est pas levé de bonne heure.
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.