There are several ways to configure your Linux distribution for the MarS Board

Take $(BSPDIR)/sources/meta-marsboard-bsp/recipes-images/image-multimedia-full/image-multimedia-full.bb as an example.

When you edit/change an existing image recipe you might not be able to commit your changes because you don't have write access to the repository where the recipe is from. You may fork that layer repo, add your own branch or write your own image recipe in your own layer .

Try a few of the following examples:

EXTRA_IMAGE_FEATURES += " ssh-server-openssh tools-sdk package-management" 
IMAGE_INSTALL_append += " i2c-tools htop git packagegroup-fslc-gstreamer1.0-full" 
IMAGE_ROOTFS_EXTRA_SPACE = "1024000" 

This is similar to the above, but changes here will affect all images that you build. And, because this file is in the build folder, your changes might get lost easily when you clean the build folder.

This is quick because only the package is built, not a whole rootfs. You may install the .rpm packages which are generated during by bitbake or even setup your own package server.

There are "Hello World" recipes in the Yocto Reference Manual and on your disk $(BSPDIR)/sources/poky/documentation/ref-manual/examples.