So, how can I make it comedy? What makes people laugh? Can anybody give me any tips?
As I said in another thread, "Comedy is the collision of reality with absurdity." Laughter is often how the human brain deals with paradox or ambiguity. This can result from contrasts as Phantom mentioned ("The bodybuilder with a falsetto or twiggy wimp with a deep basso profundo"). Or in the case of jokes, riddles and puns the ambiguity or double meaning. A visual example would be "the banana in the pocket". The audience knows the hero has a banana but the bad guy thinks it's a gun. Humor can result from the violation the expected--"The banana goes off, shooting the villain. And the hero looks surprised 'not knowing it was loaded.'" Most commonly in comedies, the protagonist takes a huge risk that initiates events that spiral out of control until the crash at the end. At that point the protagonist has learned from the previous escapades and resolves the underlying issue.
We are all funny. Many comedians have had difficult lives and so they transform that but finding irony in situations. Many will juxtaposition two concepts that are only tangentially related, develop that, then suddenly make the other match on a totally different trait.
I also distinguish between plot humor and organic humor. Plot humor is planned. Like the examples above. Organic humor is more the like quips that your characters make. They're not tangential to the story but make light of the scene. The heroes are pinned down by gun fire. The hero turns to the heroine, "Where's superman when you need him?" Heroine looks at him, "Wonder woman's savin' his ass." She gets up and starts clearing a path. This is a crime drama but the injection of humor countering the expected with the unexpected lightens the situation.
Sweetie is right, you can't teach humor. However, you can study it and get a sense of what makes a scene go from normal to absurd. As I've mentioned when that happens in a film that's supposed to be serious, it breaks the whole flow. Plot humor and situational (organic) humor have different effects.
Also, I've got an advise to "add more layers to the story". What does that mean?
Sweetie was right on the money. For many new writers, their writing is linear. In consulting on one script, the story was good but it had no nuance. The characters tend to feel flat because they are not well developed. Characters become real through their interactions with the environment, each other and the audience through backstory.
This often POs writers who are taught to think in terms of the Hero's Journey but films are not totally about the hero. "Star Wars" is often considered the prime example. However, you follow C3PO and R2D2 in the Jawa ship. You follow Han's conflict with Jabba. You follow Leia's travails. You follow Vader. Each of these are separate plot lines the interweave with Luke's adventures. The hero should only be one half to two thirds of the story. This isn't a contradiction but underscores the importance of the subplot.
What is the impact on the scientists of the stolen device? What was the villain doing before s/he learned of the device's effect? What is the impact on the janitor's friends as he's catapulted to fame? There are lots of ways, as Sweetie mentioned, to add layers or nuance to a script. Good luck!