You ask: Do we know what death is? Do we know what life is?
Death is obvious - the first death - as all living beings have observed: is a body becoming lifeless, decaying, turning to bones, and DEAD. Death needs no defining. As well, the first death defines the ‘second’ death - lifeless, decaying, DEAD.
Scripture defines death as well over and over: gone, forgotten, blotted out, destroyed, they are no more, etc.
Yes, death is defined in scripture as a process: the first death is of the body. First you go to Sheol or Abraham’s bosom (or paradise), then there is the Great judgement where the dead are separated one from another. The righteous to eternal life and the unrighteousness to eternal punishment - they are punished ‘according to their deeds’ (here they are still a living conscious spirit) and ultimately they go to the Lake of fire - the second ‘death’.
According to their deeds: Psalm 28:4, Isaiah 59:18, Jeremiah 17:10, 25:14, 32:19, Ezekiel 16:59, 36:19, 39:24, Matthew 16:27, Romans 2:6, 2 Corinthians 5:10, Galatians 6:7, Revelation 20:13, 22:12, etc.
The second death is just as the first death - it is ’death’. Then all is fulfilled. And so then the many 100 scriptures that speak of ‘death’ are fulfilled. The dead sinners are gone, forgotten, forever blotted out, as water into the ground, destroyed, perished, they are no more: Isaiah 17:14, 26:14, 60:12, Psalm 53:5, 54:5, 59:13, 88:5, 92:7, 94:23, 109:13, Job 24:20, Jeremiah 9:16, 10:20, Nahum 1:12, Job 14:12, Daniel 11:44, Zechariah 11:9, Joshua 11:12, 11:20, 24:8, Deuteronomy 7:24, 8:19, 9:3, 12:29, 32:26, Ezekiel 20:13, 20:17, 1 Corinthians 10:10, 2 Thes 2:8, etc. etc… so did God mean he would destroy them, or did God mean he keeps them alive in torment forever? I believe God means what He means - they are destroyed.
Death does not need to be described in anthropomorphic terms, neither does life. There is no ’not understanding’ what death and life are - that is, unless you prescribe to the eternal torture doctrine.