It is an aegean blue vending machine that contains the coin and dollar slots and buttons on the upper left side and the dispenser on the bottom right side. It also contains the word "candy" in orangish-yellow letters within a red rectangle. Inside there are various packs of candy that vary in color, though the only one specified is a chocolate bar.
Role in the episode
After Patrick suggests that he and SpongeBob grab a dollar bill from his pocket to replace Mr. Krabs' First Dollar which they got "permanent" paint on, SpongeBob tells him how great an idea that is and encourages him to do so. However, Patrick being his dumb self instead decides to waste his dollar on a chocolate bar from Mr. Krabs' vending machine, much to SpongeBob's anxiety, however the dollar is unaccepted from the machine twice. In both instances, a relived SpongeBob tells him to get it out so they can follow his plan, only for Patrick to force it in, which leads the machine to finally accepting the bill. After this struggle, he gets the chocolate bar he wanted.