Yes, i'm only gonna dedicate a single section to this, no point in going extremely in-depth on it, I'll try to keep basics as simple as possible, so even a new player can understand, once you get proficient with the spec, you can tailor the combo to suit your own needs, depending on the spot you're grinding.

For PvE, what we basically do, is split our PvE skill rotation into 3 sections, and connect them in right order, once you get more proficient with skill flows, you can make your own combo while keeping logical skill order, and while keeping in mind addon up-time sustain.

Scars of Dusk rotation:

Counter > Severing Thrust > Counter > Scars of the Dusk
S+LMB > Shift+LMB > S+LMB > C

Note: I always open my combos with this, it allows you to quickly cast 3 skills which means you can proc 6 addons total + Counter is 32AP buff, maximizing the DPS output for the rest of the combo, you can also use Solar Flare before scars to proc 2 additional addons of your choice.

Ling crit rotation:
Spinning slash > Jump Slash > Ground Slash - Heavy Strike 3x
S+RMB(Hold) > S +E > LMB+RMB

Note:  Heavy Strike 3x means that you do the full skill, so all 3 slashes.

Finishers:
Ground Smash > Earth Tremor / Seismic Strike >  Dusk Slash
Shift+F > Shift+F / Shift X + LMB

This is a simplified explanation on how combo'ing works on succession in PvE, it should be easy to digest if you're only starting to learn the class, once you learn the ropes, i recommend watching my video on BiS PvE combo:

Succession Warrior High-End Infinite PvE Combo

Combo:

Ground Slash - Solar Flare - Severing Thrust - Counter - Scars - Spinning 2x - Ground slash - Heavy Strike 3x - Counter - Ground Smash - Earth Tremor - Seismic Strike - Dusk Slash - Shield Charge - Counter - Severing - Counter - Scars - Spinning 2x - Ground Slash - Heavy Strike 3x - Counter - Ground Smash - Earth Tremor - Spinning 2x - Ground slash - Heavy Strike 3x - Counter - Severing Thrust - Counter - Scars - Seismic Strike - Dusk Slash - Shield Charge - Counter - Spinning 2x - Ground slash - Heavy Strike 3x - Counter - Ground Smash - Earth Tremor 

Note: This is literally best possible combo you can do for PvE on paper, please don't try to memorise it, if you don't see the pattern just by looking at the string, stick to 

Pack to Pack movement

For pack to pack movement, what you usually want to do is just spam Forward Slash and Charging Thrust, and what you can do to engage pack, is use any of the Solar Flare flows, usually Jump Slash or Scars of Dusk, then the rest of your combo the way you see fit.

What you can also do, is chain skills in a way that will allow you to pass through the pack without collision by utilizing Earth Tremor (Leap), to get back attacks from the beginning of the combo, the way you do it is:

Shield Charge > Quick Counter > Earth Tremor > Rest of the combo

W+RMB > S+LMB > F > Rest of the combo

Solar Flare > Chopping Kick > Quick Counter > Earth Tremor > Rest of the combo

W+C > S+F > S+LMB > F > Rest of the combo

• Scars of Dusk: +Movement Speed / -DP

• Severing Thrust: Back Attack Dmg / Crit Damage

• Heavy Strike: +DP / Crit Damage

• Spinning Slash: Crit Rate / +Attack Speed

• Ground Slash: +Attack Speed / -DP

• Solar Flare: +Attack Speed / Back Attack Dmg

If you manage to get a catch from distance:

• Frenzied Spear > Chopping Kick/Prime: Evasion/Shield Charge > Quick Counter > Solar Flare > Jump Slash > Shield Strike > Severing Thrust > Quick Counter > Scars > Ground Smash/Earth Tremor/Pulverize/Heavy Strike
  (Hotkey) > S+F/A or D + LMB/W+RMB > S+LMB > W+C > S+RMB > RMB > SHIFT+LMB > S+LMB > C > SHIFT+F/SHIFT+F/S+C/LMB+RMB

• Counter: +Attack Speed / Crit Damage

• Scars of Dusk: +DP / Crit Damage

• Heavy Strike: Crit Rate / Bleed Damage

• Spinning Slash: Attack Speed / Crit Damage

• Ground Smash:  +DP / -DP

• Ground Slash: +Attack Speed / -DP