Ecclesiastes 9:4-10 (WEB):
(4) For to him who is joined with all the living there is hope; for a living dog is better than a dead lion.
(5) For the living know that they will die, but the dead don’t know anything, neither do they have any more a reward; for their memory is forgotten.
(6) Also their love, their hatred, and their envy has perished long ago; neither have they any more a portion forever in anything that is done under the sun.
(7) Go your way—eat your bread with joy, and drink your wine with a merry heart; for God has already accepted your works.
(8) Let your garments be always white, and don’t let your head lack oil.
(9) Live joyfully with the wife whom you love all the days of your life of vanity, which he has given you under the sun, all your days of vanity: for that is your portion in life, and in your labor in which you labor under the sun.
(10) Whatever your hand finds to do, do it with your might; for there is no work, nor plan, nor knowledge, nor wisdom, in Sheol, where you are going.
In harmony with other verses of Scripture I believe that death is an unconscious state, like a deep sleep. Jesus described the dead as being asleep and that he had the power to wake them from that sleep - to raise them to life again.
Verse 4 says that it is better to be a living dog (they considered dogs to be the vilest of animals) than a dead lion ("The lion, which is mightiest among animals", Proverbs 30:30), i.e. it is better to be alive as the vilest of persons than to be the most noble and honourable person but dead. You can still have hope of living forever when you're alive, but there is nothing you can do when you're dead.
Verse 5 says that the dead don't know anything, consistent with having no thoughts - Psalms 146:4, "His spirit departs, and he returns to the earth. In that very day,
his thoughts perish." (Hebrew
abad, meaning perish, destroyed, vanish, be lost.)
Verse 6 says that all passions such as love, hate and envy perish (because there are no thoughts).
Verse 10 says that there is no work, plans, knowledge or wisdom in Sheol - again because you have no conscious thoughts.
Revelation 20:13-14 (WEB):
(13) The sea gave up the dead who were in it. Death and Hades gave up the dead who were in them. They were judged, each one according to his works.
(14) Death and Hades were thrown into the lake of fire. This is the second death, the lake of fire.
The Cambridge Bible notes says:
death and hell] See Rev_6:8. Sheol, the Hebrew equivalent of Hades, seems not quite determined in meaning between the receptacle of the bodies of the dead and of their souls, but is sometimes translateable as “the grave.” Here it seems implied that those who died in the sea are not in Hades, as those who were buried are: but all, whether buried or unburied, are raised and judged.
Sheol/Hades/the grave/the sea is where the bodies of dead people end up, either decomposing to dust in the dust of the earth or in the sea. I think that there is a non-physcical part to us, therefore presumably something spritual in nature, that survives in an unconscious state, probably in another dimension that is not accessable to us as physical beings, and that in the resurrection (at the beginning of Christ's 1,000 year reign) God will place that "soul" in a new body, spiritual (Christians) or human (the rest of mankind). For those (humans) judged at the end of the 1,000 years to be not worthy of eternal life, their soul will die again, and will be destroyed so it can never be brought to life again. After that there will be no more death, so verse 14 says (using the symbolism of being thrown into a fire) that "death and Hades" are destroyed.
Jesus said, Matthew 10:28 (WEB):
(28) Don’t be afraid of those who kill the body, but are not able to kill the soul. Rather, fear him who is able to destroy both soul and body in Gehenna.
1 Corinthians 15:25-26 (WEB):
(25) For he must reign until he has put all his enemies under his feet.
(26) The last enemy that will be abolished is death. [Abolished or destroyed, done away with.]