“And on the third day He rose again, according to the Scriptures; and ascended into heaven, and sits at the right hand of the Father.”
This taken directly from the Apostle Paul in 1 Corinthians 15:4, “he was raised on the third day in accordance with the scriptures.”
The must important event was the resurrection. It indicated the Jesus was successful. He redeemed humanity and bet the devil. There is some debated about whether his resurrection was a physical one or a spiritual one. The Creed does not answer this.
He “ascended into heaven” means that Jesus was no longer bodily with us. He could still appear, as he did with Paul, but not like before. Jesus is in heaven
And Jesus now “sits at the right hand of the Father.” This means that he is the right-hand man for God. He is administrating the Kingdom of God on earth.