Then the eleven disciples - Judas was dead, leaving but eleven of the original number of the apostles.

Into a mountain where Jesus lead appointed them - This "appointment" is recorded in Matthew 26:32. On what particular mountain this was is not known. It is probable that Jesus, when he made the appointment, specified the place, which has been omitted by the evangelists. Matthew has omitted many appearances which Jesus made to his disciples which have been recorded by Luke, John, and Paul. See the harmony of the resurrection at the end of the chapter.

Matthew 28:16 Parallel Commentaries

The Risen Lord's Greetings and Gifts
'And as they went to tell His disciples, behold, Jesus met them, saying, All hail.'--MATT. xxviii. 9. 'Then the same day at evening ... came Jesus and stood in the midst, and saith unto them, Peace be unto you.' --JOHN xx. 19. So did our Lord greet His sad followers. The first of these salutations was addressed to the women as they hurried in the morning from the empty tomb bewildered; the second to the disciples assembled in the upper room in the evening of the same day. Both are ordinary greetings. …
Alexander Maclaren—Expositions of Holy Scripture

Some of the Guards Report to the Jewish Rulers.
^A Matt. XXVIII. 11-15. ^a 11 Now while they were going [while Joanna and the group of women with her were on their way to tell the apostles that they had seen Jesus], behold, some of the guard [not all] came into the city, and told unto the chief priests all the things that were come to pass. [Esteeming it folly to guard an empty tomb, the soldiers went to their barracks, while their officers returned to those who had placed them on guard to report what had happened. They rightly judged that the …
J. W. McGarvey—The Four-Fold Gospel

The Great Commission Given.
(Time and Place Same as Last Section.) ^A Matt. XXVIII. 18-20; ^B Mark XVI. 15-18; ^C Luke XXIV. 46, 47. ^a 18 And Jesus came to them and spake unto them, saying, All authority hath been given unto me in heaven and on earth. ^b 15 And he said unto them, Go ye ^a therefore, ^b into all the world, and preach the gospel to the whole creation. ^a and make disciples of all the nations, baptizing them into the name of the Father and of the Son and of the Holy Spirit: 20 teaching them to observe all things …
J. W. McGarvey—The Four-Fold Gospel