Invocations which would expend a spell slot to use no longer use a spell slot.
Warlocks begins with the Eldritch Blast cantrip for free, and can choose two others, as per the PHB.
Pact of the Chain
All warlocks gain this feature, in addition to either Pact of the Blade or Pact of the Tome, at 3rd level.
Pact of the Blade
You automatically gain the Thirsting Blade invocation at 6th level, which does not count towards your total number of known invocations.
Pact of the Tome
Your tome may serve as an Arcane Focus if both your hands are free to hold the Book of Shadows.
Repelling Blast: This Invocation only affects targets sized Large or Smaller, and allows for a Strength Saving Throw to resist.
Mask of Myriad Forms: This invocation now has a prerequisite of 7th level, instead of 15th.
EDIT: The release of the new Hexblade patron for the Warlock has brought cause to adjust this QOL change. The Pact of the Blade no longer grants Medium Armor Proficiency.