And while staying with them he ordered them not to depart from Jerusalem, but to wait for the promise of the Father, which, he said, “you heard from me; 5 for John baptized with water, but you will be baptized with the Holy Spirit not many days from now.”
6 So when they had come together, they asked him, “Lord, will you at this time restore the kingdom to Israel?” 7 He said to them, “It is not for you to know times or seasons that the Father has fixed by his own authority. 8 But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.”
The book of acts tells the story of how Jesus builds His church. His first command is to wait. The disciples could have started the church by recruiting people. They could have started passing on Jesus' teaching. They could have started by doing a lot of good things - but they are all pointless without the Spirit. Jesus told them to wait for the Holy Spirit because He is where the power comes from. He is the one who convicts of sin and opens hearts to the gospel. He is the one who is building the church.
The disciples appeared to be expecting some sort of political, national kingdom. They were thinking to small. The church is going to spread way beyond the people of Israel.
Again, Jesus tells them that it starts with the Holy Spirit. He will give them power. The purpose of the power is that they will be witnesses - they will be able to tell people what they have seen and heard. They can do nothing in their own strength, they need the Spirit. But the purpose of the Spirit isn't primarily signs or wonders or feelings or miracles. It's to empower people to tell everyone on the planet who Jesus is and what He has done.