You can marshal an argument, or you might be a marshal in a sporting event, or you might be a Field Marshal, and there are many other usages but they generally are to do with organising or leading some activity.
Where does the word descend from? Well rather amazingly it originally meant someone who looked after horses. It's from early Germanic *markhaz "horse" + *skalkaz "servant". The asterisks indicate that these words are not actually attested - we don' thave them written down anywhere, so the exact words are a guess. But the first element is like "mare" and a word "scealc" appears in Old English.
The word came to us from Norman French and the French for a farrier (a smith who shoes horses) is still "maréchal-ferrant".
To conclud, here is a rather nice quote from an early printed book, courtesey of the OED.
1474 W. Caxton tr. Game & Playe of Chesse
iii. ii. 85
All maner of werkemen, as goldsmithes, marchallis, smithes of all forges.
Thanks also to RobWords for his excellent YouTube video on military titles.