Explanations from Teo are quite good.

I just want to correct some example which aren't right.

Pourquoi est-ce que tu n'es pas venu?

Je suis arrivé comme ils commençaient à manger. : that's not really native. We should say :

Je suis arrivé alors qu'ils commençaient à manger.

Tu es comme méchant! : not french. This turn of sentence isn't grammaticaly correct. When you say "so" in English (ex : You are acting so mean!) you may use "si" to insist. (ex : tu es si méchant ! = tu es tellement méchant !) 

Elle était comme suprise. We can also say : Elle paraissait surprise. (which is a better translation for "seem")

I'm not a Native speaker, nor am I very far along, but I think I can offer up an explanation that will help you understand them.

Parce que is French for "because". It's a subordinating conjunction that precedes a cause, explanation, or motive. It explains why something is done. I always like to think that it's "friends" with Pourquoi, because it's the natural answer to it. Why was something done? Because of etc.

EX:
A: Pourquoi est-ce que tu ne es pas venu? Why didn't you come?
B: Je ne suis pas venu parce que je suis malade. I didn't come because I'm ill.

Comme is used for a number of reasons. One example is to express "as" or "since". It's (another) subordinating conjunction, and it's used to show the link between a consequence and its result.
EX:
Je suis arrivé comme ils commençent à manger. I arrived as they were beginning to eat.

A second way is to express "how" or "so" as an exclamatory adverd (similar to ¡Que! in Spanish).

EX:
Comme tu es belle ! You're so beautiful! / How beautiful you are!
Comme il fait beau ! The weather is so beautiful! / How beautiful the weather is!

A third was is comme + an adjective, which is to express that something seems to be the adjective.

EX:
Tu es comme méchant! You are acting so mean!
Elle etait comme suprise. She seemed surprised.

I hope this makes it a little clearer for you! I'm sure that a native speaker could give you a more thorough explanation, but I hope that this gives you some baseline for how they're used.

Thank you both for your contributions. Here are the two sentences where I see the words used. But they seem to have the same meaning n'est pas? 

COMME la cuisine et la salle sont petites, nous avons peint larésidence avec des couleurs douces qui donne l'impression que la résidence estplus grandes

PARCE QUE la cuisine et la salle sont petites, nous avons peint larésidence avec des couleurs douces qui donne l'impression que la résidence estplus grandes