Learn Finnish: Tämä on tietysti iso helpotus meille. - This is of course a big relief to us.

It is built from the verb tietää (to know). More specifically, it comes from the adjective tietty (known, certain) plus the adverb ending -sti (which works like "-ly" in English). So it literally means something like "certainly," which we use to mean "of course."

Is the noun helpotus related to the word helppo (easy)?

Yes! Helppo means "easy," and the verb helpottaa means "to make easier" or "to relieve." By adding the noun ending -us to the verb stem, we get helpotus, which translates to "a relief."

Why do we use the form meille (to us) here?

Meille is in the allative case, which indicates movement or direction toward someone. In Finnish, just like in English, when something is a relief to someone, it is directed at them. So we say helpotus meille (a relief to us) or helpotus minulle (a relief to me).

Could I change the word order and put meille at the beginning?

Yes, Finnish word order is quite flexible. You could say Meille tämä on tietysti iso helpotus. Moving meille to the front simply places more emphasis on "to us" (meaning this is a relief specifically to us, even if it isn't to someone else).