(Note this will undergo updates since I am currently lvl 28 and only know how to do the basic summoner PvE stuff)

Summoners are a High dmg extremely squishy (ok well maybe not extremely squishy but we only wear cloth armor)character with a pet that can eat a dragon in 2 bites. Hellions are your lifeline. Your main source of damage is really up to you. You can chose between a DoT(damage over time) build or you can go with Vamp/Acidbolt for a more DPS build.

Lvl:4-10
As far as basics for low level up to 10 I would recommend getting a rank in Putrefy, blood aegis, and maxing out your hellion. Any extra talent should be saved till at least lvl 12 so you have a better idea of what you want from your class before spending them.

Lvl:10-15
This is an awkward level for summoners. You don't have enough talent points to get anything to set up a build, and you don't really have much along the lines of damage outside of your hellion. I don't know how true this is for everyone but it sucked for me. Just make sure that you put some points in Fear and a Rez(more optional for partying with people and saving them some myrrh) Fear is an extremely important skill. It will be vital to helping you out of sticky situations. The spare talent points that you have should be spent in one of 4 directions. there is a skill on your putrefy talent tree called Debilitating Plague(after 10 second target affected for 10 seconds reducing movement and speed by 50%) on your Vampirism talent tree there are 2 skills. Howl of Death (6 drops of blood: target takes X dmg and is slowed for 10 seconds) or Neurotoxin(target takes Xdmg over time)[Vital to a DoT build] and in your acid bolt tree you have actually a fifth path. There is corrosive acid in the top (deals Xdmg over time)[VItal to DoT] and you have Master Summoner (hellion gives off +X threat and deals more dmg) Whichever path you choose STICK TO IT if you try balancing you will have a major problem with your talents and you will find that you have wasted some rubies. I required a repec at lvl 26 just to survive in AT. It was not pretty.

Lvl:16-20
This area is where the summoner starts to shine. For the most part through the end of siveria you wont need a party for anything (even spec'd as bad as I was) except for the major bosses like ugluk. with your ruby points just continue spec'ing into what you were planning (or if you finished start spec'ing into another skill) Remember that Fear is a MUST for summoners

Lvl: 21-25
This is where you really have to start knowing what to do as a summoner. If you chose a DoT build then you should have either Corrosive acid or Neurotoxin by now if not both. Your tactic is run around and let the skills do their work, use your CC as often as possible. If you chose a Vampirism/Acid Bolt DPS build you will NEED to have Master Summoner rank 3 and Dark gift rank 3. Otherwise your Hellion will not be able to hold aggro, quite often my hellion doesn't hold aggro even with those skills. Dark Renewal or Plague of mending are now avaliable to you and you need to choose one or the other for now. I prefer dark renewal because there isn't a 15 second antibody that comes with the skill. If you went Acid Bolt DPS you will need to have the Blood tap skill in order to generate blood for these skills.

This brings the Guide for summoners to a close for now. I will update at regular level intervals to hopefully give a better idea of Summoners to you all.