“The apostles gathered
They told him
All that they had done
Καὶ συνάγονται οἱ ἀπόστολοι πρὸς τὸν Ἰησοῦν, καὶ ἀπήγγειλαν αὐτῷ πάντα ὅσα ἐποίησαν καὶ ὅσα ἐδίδαξαν.
This gathering of the apostles around Jesus can only be found here and in Luke, chapter 9:10. Apparently, the apostles had returned from their mission. Mark said that these apostles gathered around Jesus (Καὶ συνάγονται οἱ ἀπόστολοι πρὸς τὸν Ἰησοῦν). They told, related, or announced to him (καὶ ἀπήγγειλαν αὐτῷ) everything that they had done and taught (πάντα ὅσα ἐποίησαν καὶ ὅσα ἐδίδαξαν). Jesus had a debriefing session with his apostles where he found out what had happened to them on their missionary adventures.