Check out the complete language docs. Here are some examples to get you started:

200	A basic HTTP 200 response (this will hang).
200:da	Server-side disconnect after all content has been sent.
200:b@100	100 random bytes as the body. A Content-Lenght header is added, so the disconnect is no longer needed.
200:b@100:h"Etag"="';drop table servers;"	Add a Server header
200:b@100:dr	Drop the connection randomly
200:b@100,ascii:ir,@1	100 ASCII bytes as the body, and randomly inject a random byte
200:b@1k:c"text/json"	1k of random bytes, with a text/json content type
200:b@1k:p50,120	1k of random bytes, pause for 120 seconds after 50 bytes
200:b@1k:pr,f	1k of random bytes, but hang forever at a random location
200:b@100:h@1k,ascii_letters='foo'	100 ASCII bytes as the body, randomly generated 100k header name, with the value 'foo'.