HELP! i have lost my whole desktop

[pinkskittle17]

A few days ago I go to wake up my mac and it stays black. So i restart it. when it turns on my whole desktop is blue, absolutely nothing on it and there is no dock. i cant access the doc. somehow firefox automatically popped up on its own. i dont have that much experience at problem solving with computers but i explored the little apple in the top left corner to the fullest extent and it got me no where!
Someone pleeeeeease help.