There are four types active skills, divided by the actions the player has to do to use their effects.

Instant

Which means that skills of this type will start their effects as soon as their casting, channeling time (If applicable) has passed.They are commonly used in Metamorphosing Skills, some summons and toggleable skills.

These skills may be:

• Instant Effect: like Windwalk, Strafe that ignore the unit’s casting time, point and go off as soon as you click the button.
• With Casting time: Like Requiem Of Souls, that after activated wait for your casting point to finish and then provide their effects
• With Channeling time: Like Epicenter, Town Portal , that have to wait until the channeling time is completed to provide their effects.

Target Unit

Skills of this types will require you to select a target after clicking them to provide their effects, they are common in damage burst skills and strong disables.
They can also have Casting Time (like Sniper's Assassinate, 1.7 s) and Channeling time (like Life Drain)

• Target Unit with projectile: (Like Magic Missile, Shadow Strike) that can be avoided via Blink and Invisibility but will continue to follow units moved via forced movement (Hook, Swap, Blink Strike etc).
• Target Unit Without projectile: (Sleep, Decrepify) That can be avoided by moving outside the spell’s cast range and spell motion buffer.

Note that some spells (like Toss and Storm Bolt) uses a targeting circle, even though you must select a specific unit to target.

Target Point

Skills of this type may or may not affect the area around the casting point, some of them display a circle to indicate the area that will be affected.

• Point Target with selecting circle: (like Light Strike Array or Black Hole) will display the circle that helps better aiming for the skill.
• Point Target without circle: (like March of The Machines or Teleport) that will only use the small reticle to aim the skill.

Target Unit or Point

This is used by a few skills, it allows the ability to be casted on any point or on specific units. Some examples include:

• Meat Hook
  
• Fissure
  
• Timewalk

Note that skills during the cast time can be canceled with the “stop” order and when you are interrupted casting them they don’t go into cooldown or consume mana. This unlike skills in channeling time, that will make you lose the mana and will go into cooldown.