So, you want to be an Existentialist, eh?  You might want to rethink that.  According to Linda Seligman's textbook, there are 4 major dimensions of Existential Theory, all relating to the basic principle that life is hard for a human being, has no meaning in and of itself, and we will spend a great deal of our time in sadness.
    (1) We know from early in life that death is inevitable for all human beings, no matter how wonderful we are.  Therefore, we are frequently depressed by the thought that no matter what we do, and how well we do it, we'll eventually just end up dead.
    (2) We are ultimately totally alone.  No matter how well any other person thinks they know us, they really do not know exactly how we feel, or exactly how we think.  So there we sit, in a room full of people, and yet we are all alone.
    (3) Everything is meaningless.  Everything we do will eventually be washed away by the ocean of time, therefore there is no purpose to our struggles, and we effectively make no difference at all.  Life is a series of random events, and no matter how hard we try to make some sense and pattern out of it, we eventually discover that it had no real meaning at all except to occupy our lifespan.
    (4) Anxiety - a deep, disturbing, constantly-gnawing anxiety - is with us all the time.  Knowing the above 3 things, we realize that the only thing we can do is accept responsibility for creating our own meaning in all this mess, and making our lives something worthwhile.  Our frequent failure to be our absolute best and most productive makes us feel guilty about wasting our existence, causing our anxiety to increase.
    From the above, you can see why Existentialists believe that it is absolutely necessary for all of us to engage in therapy, with someone who will help us deal with all the pain of life, create meaning out of our own personal mess, accept responsibility for our failures, and connect with other people in a deep and spiritual way.

    If you are still interested in Existentialism, you can discover a lot by reading the opinions of the authors and philosophers mentioned on the Humanist page.

ASSIGNMENT:
~  Find a mirror, look deeply into it, and repeat the following:  "I am a good and decent person.  I will die someday, but not soon, and I plan to make the best out of every day between now and then.  I have plenty of good people in my life who care a lot about me.  They may not understand me fully, but that's OK because I don't get them all the time either.  I'm having a positive impact on many people around me, and that's like having a positive impact on the rest of eternity.  I may fail sometimes, but I really am trying pretty hard to be a good person, so there's no point in worrying over it a lot, when I can actually do something like go out and be nice to someone.  Most of all, I feel great because I'm not an Existentialist." 
Now, get off this page, and get busy doing something positive and productive.