And from Mark's gospel:
Mark 3:14-15 New Revised Standard Version (NRSV)
14 And he appointed twelve, whom he also named apostles, to be with him, and to be sent out to proclaim the message, 15 and to have authority to cast out demons.
In the area where Jesus had been performing the miracles, there was a mountain.
Jesus managed to dismiss the crowd for a time, since he wanted to gain assistants and successors in his ministry. On this hill they'd be undisturbed, and he'd have leisure to give them the information concerning the call given them at this time.
He called to him those whom he wanted; he chose from the total number of his missionaries.
And as he chose them, they came to him in a place apart from the others. He then constituted twelve missionaries as a body for themselves.
Jesus' charge to them consisted in these points: That they should be with him, should be sent out by him and should have power to cast out demons.
The 12 were thus called, and they received their charge. And their names are recorded in order.
There was Simon Peter and James and John. These three are mentioned first, because they were Jesus' friends, being with him both on the Mount of Transfiguration and also in Gethsemane.
There was Andrew, Philip and Bartholomew, Thomas, James, Thaddaeus and Simon.
Last is mentioned Judas, the traitor, who was let into the 12 that prophecy might be fulfilled.
Their charge having been made to them, the 12 returned to the valley with Jesus, and entered into a house. They needed rest and recreation, the last days having been strenuous.