This was a slightly surprising question, but the context made it more clear. The person who asked this was from a country where the historic pattern has been animism and ancestor worship. There is a Chrsitian presence in the country, but it is a small minority. Religion in general had been neglected and discouraged culturally starting when the questioner's parents were small children.
What do Christians do in church? We gather, as we believe, in the presence of God who visits us in the actions of the church service. We sing some songs related to God's attributes and the things he does. We read from the Bible, which we understand as God's words for us. We hear someone explain a part of the Bible and why it matters. We pray that God will guard his people. We receive communion, a ritual in which we believe God feeds us with forgiveness and in which he is present with us.
There's a follow-up question, though. "I mean, why do Chrsitians do this when they go to church? What do they accomplish?" About this time in our conversation I was wishing several things. First, that the questioner had not spent about the last 30 hours in transit. Second, that I could speak his native language. Third, that it wasn't nearly 1 in the morning on a Sunday morning. I didn't think his jet lag made a good prospect for saying, "Let me pick you up in about 7 hours, we'll have breakfast and go to church."
Why do Christians go to church? We believe that in the divine liturgy, as it has been celebrated in much the same way for nearly 20 centuries, God meets with his people. He gives them forgiveness for their wrongs. He nurtures their faith through his word, which gives life and salvation. He gathers his people and their resources so they can change the world as he would have it. He gives forgiveness and hope through his body and blood given for his people.
There are lots of additional benefits to be found in a church service: friendships, a chance to pray for others and be prayed for, a series of social norms, a sense of belonging. But in the end, we assemble to be with Jesus, according to His word. That's why we really go to church.