Search examples:

needle
search for "needle"
thread or needle
search for either "thread" or "needle"
class needle
search for files containing both "class" and "needle"
class Needle
search for files containing both "class" (case insensitive) and "Needle" (case sensitive)
class Needle case:yes
search for files containing "class" and "Needle", both case sensitively
"class Needle"
search for files with the phrase "class Needle"
needle -hay
search for files with the word "needle" but not the word "hay"
path file:java
search for the word "path" in files whose name contains "java"
needle lang:python
search for "needle" in Python source code
f:\.c$
search for files whose name ends with ".c"
path -file:java
search for the word "path" excluding files whose name contains "java"
foo.*bar
search for the regular expression "foo.*bar"
-(Path File) Stream
search "Stream", but exclude files containing both "Path" and "File"
-Path\ file Stream
search "Stream", but exclude files containing "Path File"
phone r:droid
search for "phone" in repositories whose name contains "droid"
phone b:master
for Git repos, find "phone" in files in branches whose name contains "master".
phone b:HEAD
for Git repos, find "phone" in the default ('HEAD') branch.

To list repositories, try:

r:droid
list repositories whose name contains "droid".
r:go -r:google
list repositories whose name contains "go" but not "google".