Genuine degrees are embossed and have a gold seal and if you bring the certificate against a bright light, there should be a hologram watermark visible. The signature should also not be printed, as genuine certificates have signatures which are written in ink and they do not contain any spelling mistakes.
To verify a certificate, a browser will obtain a sequence of certificates, each one having signed the next certificate in the sequence, connecting the signing CA’s root to the server’s certificate. This sequence of certificates is called a certification path.
Apart from legitimately graduating from a university, there are only two ways to obtain a degree certificate. You can either buy a real certificate from a fake university, or buy a fake certificate that pretends to be from a real university.