This will display the Bash help (manual) page for the specified built-in.
For example, help unset will show:
unset: unset [-f] [-v] [-n] [name ...]
Unset values and attributes of shell variables and functions.
For each NAME, remove the corresponding variable or function.
-f treat each NAME as a shell function
-v treat each NAME as a shell variable
-n treat each NAME as a name reference and unset the variable itself
rather than the variable it references
Without options, unset first tries to unset a variable, and if that fails,
tries to unset a function.
Some variables cannot be unset; also see `readonly'.
Returns success unless an invalid option is given or a NAME is read-only.
To see a list of all built-ins with a short description, use