I've found the short guide to "Program evaluation basics" helpful to me.
You can start with "why evaluate in the first place?" and continue with
"Efficiency, effectiveness and impact," "The 'Program Impact Model',"
and a glossary and a short list of recommended reading.
I especially appreciated the diagram at
https://meta.wikimedia.org/wiki/Program_evaluation_basics:_the_program_impact_model . I like having words for the different parts of evaluation, especially
to clarify the difference between inputs and activities, between outputs
and outcomes, and between outcomes and impact. For instance, my group
has, in the past, found that our outputs from specific events or other
activities were reasonably adequate, but didn't lead to sufficient
outcomes, or to impact.