To unlock the following, you have to play the game and collect/Earn achievements. You can find those earned achievements in your Game-Main menu or you can view them if you signup at one of the Steam communities.

Achievement	How to unlock
Amuse-Bouche	Eat the final cork in Level 1.
Blob Friends Forever	Collect all Blob Friends in the game.
Delicious Magnetic Balls!	Eat the magnetic balls at the end of end of Chapter 5.
Extinction	Eat all of the escape pods in the final level.
Finally, monsieur, a wafer thin mint	Absorb 1500 objects.
Galaxicide	Eat the solar system.
Getting the Boot	Boot yourself over the spikes at the end of Chapter 4.
Golden Blob	Earn a gold medallion in every level.
Graduation Dinner	Eat the valedictorian at the end of Chapter 1.
Houston, we have a problem	Board the rocket ship at the end of Chapter 2.
It Came From Outer Space	Take a ride on the space elevator at the end of Chapter 3.
Jealous?	Look up the top score on any leaderboard.
Mini Master	Complete all of the Mini-Game levels.
Not too Shabby	Earn a silver medallion or better in five levels.