In a BitBake recipe file (.bb), there are a few mandatory fields and 
variables that need to be included. These essential components provide
metadata and define the recipe's behavior. Here are the mandatory items
typically found in a .bb file:

Recipe Information:

SUMMARY: A brief description of the recipe.
DESCRIPTION: A detailed description of the recipe.
LICENSE: The license under which the recipe is distributed.
LIC_FILES_CHKSUM: The checksum of the license file to ensure it hasn't been modified.
SECTION: The section or category to which the recipe belongs (e.g., "base", "utils", "libs").
Recipe Identification:

PR: The recipe revision number. It helps identify changes or updates to the recipe.
Source and Version Information:

SRC_URI: The source URL or file location of the software or source code needed for the recipe.
SRCREV: The specific revision or commit of the source code to use.
PV: The version number of the recipe.
Dependency Information:

DEPENDS: The list of other recipes or packages that need to be built before this recipe.
RDEPENDS: The runtime dependencies required by the recipe at execution.
Build and Installation Instructions:

do_configure(), do_compile(), do_install(): These functions define the necessary actions during the configuration, compilation, and installation stages of the build process. They contain the corresponding commands or tasks required.