Soldiers on guard roar and sing horribly (8)
I believe the answer is:
garrison
'soldiers on guard' is the definition.
'garrison' can be an answer for 'guard' (thesaurus). I'm unsure of the 'soldiers on' bit.
'roar and sing horribly' is the wordplay.
'and' is a charade indicator (letters next to each other).
'horribly' is an anagram indicator (a horribly wrong version of the letters).
'roar' put after 'sing' is 'singroar'.
'singroar' with letters rearranged gives 'GARRISON'.
Can you help me to learn more?
(Other definitions for garrison that I've seen before include "troops in base" , "Military stronghold" , "Military fort" , "Military base" , "Roarings (anag.)" .)