The main purpose of the Marksmanship is to deal major amounts of ranges damaged, and it does so by increasing the overall damage of the Hunter, using talents such as Ranged Weapon specialization, Lethal Shots and Mortal Shots, and bonuses to specific damage skills-such as Barrage and Improved Stings. And also it offers an additional high-yield skill, the Aimed Shot, which can deal massive amounts of damage.
Primarily, Beast Mastery talent tree focuses on increasing the power leveling damage output, and the tanking ability of your pet. A fully buffed pet will have the tanking and damaging potential approaching that of a feral druid. This is one of the more popular talent trees for use when the hunter is leveling because it allows you pet to hold aggro well, tank, and deliver lethal damage, especially to casters.
In general, the survival tree is considered to be a "utility" oriented tree. It emphasizes a more defensive and utilitarian overall strategy, it is designed for the "worst case scenario", for a hunter, is being forced into a melee fight. From the beginning, talents that increase damage via melee attacks contrast with the ranged talents of the marksmanship tree, or the pet buffs of the Beast Mastery tree, allowing you to stay out of melee combat all together. However, near the middle and further downward, this tree moves in an entirely different direction, breeding one of the deadliest (if rarely used) character builds in the game.
On the hand, it is important to learn to command your pet effectively. Whenever one of your pets is out a "pet bar" will appear above your normal action bar. This is your main interface for interacting with your pet. When you train your very first pet, probably there won't be very much on there besides the basic commands; Attack, Follow, Stop, and Aggressive, Defensive, and Passive. 
On the other hand, training points can augment a pet. Pets can be trained to have higher health or armor class, as well as all the major classes of resistance (Arcane, Fire, Nature, Frost, Shadow). There are other offensive and defensive skills available. Some are taught by a pet trainer, which are found in most major cities. Others are learned as the Hunter journeys around the world. Some pets have extra skills once you've tamed them, and after using that pet in combat for a few minutes, you'll learn that skill, and will be able to pass it on to any of your other pets that can learn it.