Using a weapon of any kind in a competent and confident manner implies aggressiveness in pursuing one’s goals. Using a weapon clumsily is a sign that the dreamer doubts his ability to attain his goals.
Being threatened by a weapon hints that the dreamer feels that everyone is against him. Whether or not that is true, and if true, what the solution is, can be deduced from other symbols in the dream.
Astrological parallel: Mars Tarot parallel: The suit of swords