Hi @jchdel!
Many people find Yocto a bit challening in the beginning.
So even though this is not strictly related to Mender, we do have a forum category with taking the first steps with Yocto here: https://hub.mender.io/c/tutorials/yocto-project
In particular, this might cover what you are looking for: https://hub.mender.io/t/how-to-install-packages-in-yocto-project
Let us know how it works out!