Both Lamb and Wolf mark targets to hunt. Lamb marks an enemy champion for death (this mark activates after an 8 second delay), while Wolf periodically marks monsters in the enemy jungle. All champions can see which targets are marked.
SPACESPACESp. After 50 seconds of having no active jungle mark, Wolf marks an enemy jungle monster for 3 minutes.

Wolf marks jungle monsters based on Kindred's current stacks:

0 Marks: Rift Scuttler
1-3 Marks: Rift Scuttler, Crimson Raptor, Gromp
4-7 Marks: Red Brambleback, Blue Sentinel, Ancient Krug, Greater Murk Wolf
8+ Marks: Rift Herald, Baron Nashor, Elemental Drakes, Elder Dragon

If Kindred kills a marked target or assists in their death, they gain a mark. Kindred's basic attacks and Mounting Dread gain 75 range at 4 stacks, plus 25 range every 3 stacks thereafter. Stacks also amplify Kindred's basic abilities:

Q - Dance of Arrows: Bonus attack speed increased by an additional 5% per stack.
W - Wolf's Frenzy: Current health damage increased by an additional 0.5% per stack.
E - Mounting Dread: Missing health damage increased by an additional 0.5% per stack.

Targets successfully hunted cannot be targeted again for 240 seconds. Lamb can also change her target after 90 seconds if the target hasn't died in that time.
Whilst marks boost things like AA range and damage of abilities they are not a necessitiy on Kindred and you should not die for a mark because if you get behind on farm that will be worse than being behind on marks. To get and easy first mark follow the jungle pathing of Buff>Wolves>Buff>Scuttler as Wolf always marks a Scuttler at 2:30