Conference Calls have been a pretty basic feature for a while now. When you've dialed a number and the recipient has answered, at the top of the dialer keypad there should be a little phone icon with a + in it. Tap on that to dial your secondary caller and when they answer you should merge them so all three of you can talk to each other. Better details here: https://www.wikihow.com/Conference-Call-on-an-Android