This is the 257th most frequent Russian word.
касается
"Pertains to" or "relates to."
Here, "касается" is used to introduce a topic or subject of discussion, translating to 'regarding' or 'concerning'.
Что касается климата, наш регион имеет мягкую погоду.
Regarding the climate, our region has mild weather.
In this sentence, "касается" conveys relevancy or impact upon someone or something, translated as 'concerns' or 'affects'.
Эта проблема касается всех нас.
This issue concerns all of us.
Here, "касается" and its derivative are used in the literal sense, describing physical contact, translated as 'touch'.