https://openwrt.org/docs/guide-developer/build-system/use-buildsystem



Typical actions:

    git checkout <branch/revision/tag> when you don't want HEAD.
    make menuconfig and set target.
    make defconfig to set default config for build system and device.
    make kernel_menuconfig (optional :!: it's highly likely that kernel modules from the repositories won't work when you make changes here).
    make menuconfig and modify set of package.
    make download (download all dependency source files before final make, enables multi-core compilation).
    scripts/diffconfig.sh > mydiffconfig (save your changes in the text file mydiffconfig).
    make start the build process.