adverb
at first; to begin with; as a first step
Used when starting something, often introducing the first action in a sequence. Common in both spoken and written Japanese.
手始めに、自己紹介をしましょう。
To begin with, let's introduce ourselves.
手始めに簡単な問題から解いてみてください。
As a first step, please try solving the easy problems.
Compound of 手 (hand, method) + 始め (beginning) + に (adverbial particle). Literally 'at the hand-beginning', i.e., as the first practical step.