You are only allowed to ask one question rather than several on enotes. I have edited your question accordingly and will focus on the theme of this poem.
I think the biggest theme that emerges from this carefully constructed poem is the idea of how we meet death and face it in our lives. Dylan of course is addressing his father as he is dying, and if we read the poem carefully we can clearly see how he is encouraging his father to meet death head on:
Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage, against the dying of the light.
Thus the cry of Thomas if for his father to not submit quietly to death, but to "rage" against it even though their submission to death is inevitable. Thomas continues the poem by referring to four kinds of men who all find reasons to rage against the coming of death. This then culminates in the moving and defiant last stanza, as Thomas explicitly addresses his father:
And you, my fahter, there on the sad height,
Curse, bless me now with your fierce tears, I pray.
Do not go gentle into that good night.
Rage, rage against the dying of the light.
The main point of this poem is therefore that all people should try to find some way to fight against death.