Abilities

Abilities are special skills that all Warframes possess, whose abilities allow them to turn the tide of battle. Every Warframe has a set of four select Abilities unique to them, that can determine the type of role and fighting style that a Warframe is most effective at; for instance a Frost's power set that slows down enemies and defends allies from attack make him ideal for defensive play, while Nova with her damage power set is more suited for offensive play. All powers serve their purposes so stock up on your Warframes.

Warframe powers require Energy, which is spent every time a power is used. While there are various methods for Warframes to recover energy, a Warframe only has a limited energy capacity, thus power use must be carefully managed to prevent running out of energy at critical moments. Different powers have different energy costs upon casting, with more powerful abilities requiring more energy.

Types
Warframe Abilities are currently officially classified into four different types, according to their function:

Damage
The most common type of power set in the game; Damage type powers deal direct damage to enemies, making them the ultimate offensive abilities.

Buff & Debuff
This subset of powers are used to modify a unit's innate stats. Buff type powers enhance a Warframe or their allies, while Debuff powers weaken or cripple enemies. Some abilities can even perform both at the same time.

Mobility
Mobility powers enhance a Warframe's ability to travel between two points, or allow them to reach normally inaccessible places.

Perception
Perception powers are used to confuse or distract enemies, making them engage false targets, or prevent them from seeing the player entirely.

Certain Warframe powers can be have two different classifications, for example a power that can be both a Buff/Debuff and a Damage power at once. Currently, the above classification of powers is used to determine which powers are affected by certain enemies, such as Corpus Combas.

Ability Mods
Warframes Abilities can be affected by four types of modification: Ability Duration, Ability Efficiency, Ability Range, and Ability Strength. With the proper combination of mods and gear Abilities can obtain a maximized value. See Power Mods and Abilities

Ability Duration
These mods affect how long a Warframe ability lasts. A good frame that benefits greatly from power duration is Mirage, as most of her abilities benefit greatly by being longer and besides her Prism ability, sees little drawbacks.

Mods that affect Ability Duration positively:

Maximized at +182% with a negative effect of -66% range. Note that Continuity and Primed Continuity are mutually exclusive, thus maximized value assumes the use of Primed Continuity.

Ability Efficiency
These mods affects how much a Warframe ability costs to cast. Ability Efficiency has a hard cap of 75%: an ability which costs 100 energy cannot be reduced below 25 energy.

Mods that affect Ability Efficiency positively:

Maximized at +90% with a negative effect of -60% duration. Because of the hard cap mentioned above, it is objectively useless to completely level Fleeting Expertise as well as Streamline in the same build unless also utilizing a mod that decreases Ability Efficiency, such as Blind Rage, or minimizing the drain of channeled abilities with as few mods as possible.

Ability Range
These mods affect the radius and targeting range of Warframe abilities.

Mods that affect Ability Range positively:

Maximized at +150% with a negative effect of -60% Ability Strength

Ability Strength
These mods affect the damage and the 'potency' of Warframe abilities (such as Banshee's Sonar and Energy restored by Trinity's Energy Vampire).

Mods that affect Ability Strength positively:

Maximized at +199% with a negative effect of -55% Ability Efficiency and -27.5% Ability Duration. Maximizing together with a maxed Fleeting Expertise on a frame that does not need much duration is a good tactic, since it will effectively triple the damage of your skills and also make it 5% cheaper to cast (although it will require 4 mod slots in your frame).