TL; DR: Product Backlog Refinement
Where to start when kicking-off an agile transition?
Usually, tools and processes are smallest the common denominator among all participants, as they are at the core of the grand scheme of agile things.
It is a rare occasion that you start from scratch with a brand-new team without an existing product, probably even in a more or less nascent organization, for example, a startup.
In most cases, an existing product delivery organization with available products, and services will go “agile“. In this case, turning attention to the available product backlog is a pragmatic first step. The following process describes what aspects need to be attended to optimize the outcome.