What exactly IS existentialism?

http://www.iep.utm.edu/existent/

"Existentialism is a catch-all term for those philosophers who consider the nature of the human condition as a key philosophical problem" 

"A key idea here is that human existence is in some way 'on its own'"

"The next key theme is freedom. Freedom can usefully be linked to the concept of anguish,"

"Although the natural world can apparently be understood by physical science or metaphysics, this might be better thought of as 'description' than either understanding or explanation."

The rest of the movement's ideas don't really speak to me.

Key ideas that seem to resonate with me: 

• Human existence is on its own.
• Anxiety/Anguish
• Doomed to be free
• Life is completely of your own making.
• The result is inescapably absurd.

Food for thought.