bitbake SRC_URI file://

Also you can edit .bb file as follows,

FILESEXTRAPATHS_prepend := "path_to_home_folder_of_source_folders:"
SRC_URI = "file://Source_floder/*"

as an example

FILESEXTRAPATHS_prepend := "/home/username/:"
SRC_URI = "file://tarballs/*"

Well, if you want to fetch from a local directory, use e.g.:

SRC_URI = "file:///home/user/tarballs/helloworld.tar.gz"

The FILES and FILESEXTRAPATHS variables tells bitbake where to find files which are referenced as:

SRC_URI = "file://helloworld.tar.gz"

These files are searched for in the locations specified by those two variables. (Or rather, FILESEXTRAPATHS is searched and then some possible subdirectories of the directories specified in FILESEXTRAPATHS, amongst those the expanded values of DISTRO, MACHINE, ARCH, etc).

FILES (and FILESEXTRAPATHS) are used to find files stored together with the meta-data, i.e. under the paths meta-/recipes-/name/XXX.

See http://www.yoctoproject.org/docs/1.7/mega-manual/mega-manual.html#var-FILES and http://www.yoctoproject.org/docs/1.7/mega-manual/mega-manual.html#var-FILESEXTRAPATHS

Better you can keep your files in present(where the .bb file present) directory and give the below lines in your .bb file.

FILESEXTRAPATHS_prepend := "${THISDIR}:"
SRC_URI = "file://helloworld.tar.gz"

FILESEXTRAPATHS_prepend : tells to bitbake the files are present in where the .bb file is present.