Thank you very much. Could you please help me check these sentences?

1)In the second stanza there is the description of a gas attack toward the trenches: a white fog raises up suddenly. While the poet manages to wear the gas mask, someone isn't fast enough, and the poet sees him die through the green mask pane.
2) Anyway, in the third stanza he asks to himself if the reader would be able to understand how it feels to walk in a wagon where the dead and sick soldiers had been thrown.
3) Additionally, he remembers the face and the eyes of his friend while he was trying to breath with his lungs filled of blood.
4) At last, in the fourth stanza he end his description of the evilness (??) of the war, and says that he won't tell to his children the old lie, which defines war as glorious and wit (???)
5) While Lord Henry meets Dorian, he is captured by his beauty and youth, so he explains to the boy his concept of beauty.

1)In the second stanza, there is the description of a gas attack on the trenches: A white fog rises up suddenly. While the poet manages to get his gas mask on, someone else isn't fast enough, and the poet sees him die through the green mask panes.

2) In addition, in the third stanza he asks himself if the reader would be able to understand how it feels to walk behind a wagon where the dead and wounded soldiers had been thrown.

3) Furthermore, he remembers his friend's face and eyes while he** was trying to breathe with his lungs filled of blood.
(How will you clarify whether this "he" refers to Owen or to his friend?)

4) At last, in the fourth stanza he ends his description of the evil of the war and says that he won't tell his children the old lie, which defines war as glorious and sweet. (dulce = sweet; decorum = fitting -- http://www.archives.nd.edu/cgi-bin/lookup.pl?stem=decor&ending=um )

5) When Lord Henry meets Dorian, he is captivated by his beauty and youth, so he explains to the boy his concept of beauty.

While -- conveys a meaning of an ongoing event
When -- conveys a time in the past when something happened (not ongoing)

Anyway = too casual for academic writing, and shouldn't be used as a transition word except maybe in dialogue.

Here are the corrections for your sentences:

1) In the second stanza, there is a description of a gas attack towards the trenches: a white fog suddenly rises up. While the poet manages to wear a gas mask, someone isn't fast enough, and the poet sees him die through the green mask pane.

2) Anyway, in the third stanza, he asks himself if the reader would be able to understand how it feels to walk in a wagon where the dead and sick soldiers have been thrown.

3) Additionally, he remembers the face and the eyes of his friend while he was trying to breathe with his lungs filled with blood.

4) Finally, in the fourth stanza, he ends his description of the evilness of war and says that he won't tell his children the old lie that defines war as glorious and wise.

5) While Lord Henry meets Dorian, he is captured by his beauty and youth, so he explains to the boy his concept of beauty.