How many different types of certificates are on my Android device?

Like any other computer systems, your Android device can have 2 main types of certificates:

1. Trusted CA Certificates - Certificates that represent Certificate Authorities (CA). There is no way to verify a CA certificate. You need to trust it and allow Android to use it to verify other certificates. This is why it is stored on your device.

For example, "DigiCert" is a trusted CA certificate. When you visit Twitter web site, your Android system uses "DigiCert" to validate Twitter's certificate.

2. Personal Certificates - Certificates that represent yourself or your device. A personal certificate is your own property. You need to present it to other systems to identify yourself or your device. This is why it is stored on your device.

For example, your network administrator may provide you a personal certificate for you to access the Wi-Fi. You need to install it on your Android device and use it to make a Wi-Fi connection.