Heaven is heaven because of the presence of God.
As the Psalmist says, we can find the fullness of joy and pleasure in His presence.
Psalm 16:11 - Thou wilt show me the path of life: in thy presence is fulness of joy; at thy right hand there are pleasures forevermore.
The Bible doesn't give a clear idea about all that we would do in Heaven. However, we know for sure that we would be with Jesus, serve/worship God and will be free from pain, tears and sins. Yet, for a terrible sinner like you and me, who deserves Hell, an entry into Heaven itself is a great gift. But, remember that our God is abundant in wisdom and loving-kindness. If the temporal world with all the curses of sin and evil is this beautiful and amazing, how much more awesome will heaven - God's dwelling place be?
Revelation 22:3 No longer will there be any curse. The throne of God and the Lamb will be in the city, and his servants will serve him.
Revelation 21:4 - And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away.
How to be sure of being saved or going to heaven after death?
Believe in the ONE True Triune God(Father, Spirit, Son) and that Christ came down to earth as a man, died on the cross and bought our pardon, and is risen on the third day. Accept Christ ALONE(not self-righteousness, not Mary, not Saints, not religion, not sacraments) as your personal Savior.
We are saved by GRACE, through FAITH, in CHRIST ALONE.
A disobedient believer will usually be chastened or disciplined by God in this life and lose rewards in heaven.
Jesus is the Only Way to Heaven