Hunter's Mark as a feature/resource

Quote from Duskforme_Lycanrock >>

Will someone dumb hunters mark down. My ranger has it. I want to know the mechanics. 

 Can't imagine you need the help a year later.  But, it looks like no one answered the question.

Dumbed down version:
Use it as often as you can and start with your free casts.  Place it on the target you want to focus down.  Hit them until they die, then move it to your next target.  Each weapon attack against the target will do 1D6 extra damage.  If you do more attacks on the marked target you'll do more damage.  Be careful with concentration spells.

The overly detailed version:
The spell is a concentration spell (you can only concentrate on one spell at a time).  It's cast a a bonus action and it targets one creature.  It also lasts a pretty long time, so a single class can often last for two combats.  When you hit that target with a weapon the target takes 1D6 extra damage.  As a bonus action you can move that mark to another target to apply the extra damage there.

As a ranger you get free casts of this each long rest.  This is your favored enemy ability.  When you cast it without using a spell slot it ALSO means you can cast another spell that does use a spell slot that round.  This can be effective.  It's extra spells you can cast each day which is a pretty big deal on a half caster class like ranger with fairly few spell slots available.

Mechanically, to make the most of hunter's mark you want to be able to increase the number of weapon attacks you have against that target.  You can do this with nick weapon mastery, or two weapon fighting, you can do this with extra attack.  You can also do this with bonus action attacks and reaction attacks.  Additionally, things that eat up your bonus action can make it harder to make the most of the need for you to spend a bonus action to move the mark.  Lastly, the concentration can be an issue.  You can only concentrate on one spell at a time.  This may mean you need to drop your hunter's mark to do something else.  This generally isn't too much of an issue because you have so many free casts that just ... casting it again is rarely an issue.  Most of the ways to increase your attack output will involve a strength based build.  So, this spell is stronger on strength based characters than dexterity based ones.

Another thing to do know is that a lot of people who don't seem to understand game mechanics very well are VERY passionate about hating the hunter's mark spell. 

A quick example of the value of increasing attacks -
If you do one attack per round you do 1D6 damage.  avg 3.5.  
If you can increase that to two attacks per round you DOUBLE this to 2D6 damage.  avg 7 damage.

So at level one using the weapon mastery you can have for nick means you can attack twice per round without the 5th level extra attack feature.  That's likely what you want to use to maximize damage output.  Nick from a dagger can be used with a melee attack or a thrown attack for versatility.  Dagger, throwing hammer, and handaxe are all options that work well together.

Two weapon fighting even without nick mastery can weaponize your bonus action. The nick attack essentially moves this bonus action attack to your attack action to free up your bonus action (which is a big deal).

Feats like dual wielder give an extra bonus action attack, so does polearm master, so does great weapon master (this is trickier to make work, but it can work).

Feats like polearm master and sentinel give you an attack with your reaction where sentinel triggers more often, especially if you're using a weapon with reach.

Cleave can give an extra attack, but it's to a target other than the one you just hit which means you wouldn't apply hunter's mark.  The hunter subclass has a horde breaker ability that works in a similar way.

It's possible for a 5th level ranger to attack 8 times in a round and for 5 of those attacks to be against the hunter's mark target for 5D6 damage coming from a first level spell that didn't even cost a spell slot.   Any ranger is capable of doing 5D6 hunter's mark damage in a round if you build for it.  Or ... you could use a longbow and do 2D6 damage per round with it from level 5 and beyond.