Hans is a pinkish white hand, with the fingers folded together. His sleeve can be presumed as part of a naval jacket (Which would make sense, considering the theme of the show). He has a deeper voice.
In the theme song of the show, he can be seen briefly, handing SpongeBob his pants. His first role in the show itself was in "Suds," where he made appearances in cut scenes, where he used SpongeBob and Patrick as cleaning tools.
In "Imitation Krabs," SpongeBob realizes how he chose the wrong Mr. Krabs, and goes out to retrieve the real one, which he had covered with Tartar Sauce and served with fries. However, upon exiting the Krusty Krab to retrieve him, he sees that Hans is trying to eat him with a fork. When SpongeBob grabs the cart and wheels him in, Hans disappears into the sky. Whether that was a different German hand or Hans was mysteriously above water and gigantic, is unknown. His third appearance was in "Clams," when Mr. Krabs, during his breakdown, he sucked on Hans' thumb.
Hans made a famous appearance in the episode "Model Sponge." In this episode, Hans is the hand that can be seen in the New Sponge commercial. He uses SpongeBob to scrub dirty surfaces. However, SpongeBob resists Hans when he wants to clean the grotesque toilet with him. Later, when SpongeBob goes to work at the Krusty Krab again, Hans can be seen using the bathroom there. Why Mr. Krabs would allow him in his establishment after the events of "Imitation Krabs," and how a severed Human Arm can use the restroom, is unknown.
In The SpongeBob SquarePants Movie video game based off the movie, whenever SpongeBob or Patrick fall or drift off course, or fail to make it to a checkpoint or area on time when riding in vehicle, Hans catches them and they respawn back on course to retry.