I don't quite understand what the difference is between TLS and a certificate. TLS secures the transmission by encrypting the data. So normally no man in the middle attack is possible and nobody else can read it.
What is the certificate used for? When does this come into play? What does the certificate do technically? Or is a certificate only there to confirm that the website is really trustworthy and belongs to the person you think it is? I don't quite have an overview here.