"Green slopes"? Grassy hillsides.
"Paraded"? Marched up and down.
About what time has elapsed between the incident of the first stanza and that of the second? Probably a week or thereabouts.
What deed is referred to in the first stanza? The seizure of the hill.
What is meant by "idly walking"? Without any definite purpose in view.
"Marked"? Noticed.
About what were the veterans probably "talking"? About their military exploits in years gone by.
What words are suitably used in describing these veterans? "Trembling" and "gray" suggest old age.
Arrange "their trembling heads and gray" in ordinary prose order. Their gray and trembling heads.
Why should the veterans be filled with "pride"? Because of the brave deeds they had done.