Activate text to speech
It sounds like you talking about TalkBack, the accessibility program that comes with a lot of Android devices.

In order to activate TalkBack (assuming it is installed), open your phone settings, then go to the Accessibility section. Select TalkBack and enable it (and accept the warning that TalkBack will be able to see sensitive information).

After it is enabled, you should look through the settings for TalkBack and configure it to your needs.