Twilio incoming/outgoing call as confererce

Question

When I make/receive call on twilio and I understood that in order to do those 4 actions(Call, Hang up, put onhold and unhold calls, barge) I need to create a conference call, but I don't understand how I add my Twilio number to the conference and how do I add another number of a mobile of a client. For example, if my Twilio number is "nnnnnnnnnn" and the customer's I want to call to mobile number is "xxxxxxxxxx" – I  : 1. Calling the customer(from Twilio number " nnnnnnnnnnnn" to mobile number "xxxxxxxx") 2. Hold the call,parking,barge,Pooling 3. UnHold the cold 4. Hangout the call. 5. Add many used both end income or outgoing.

Note: Only need in conferene incoming/outgoing calls.

Please suggest for it.