After moving to a new city, he threw himself into volunteering to meet people and feel connected.

threw 是动词 throw 的过去式，throw 本意是"投掷、扔"。 himself 是反身代词，指"他自己"。 into 是介词，表示"进入...状态"或"朝向...方向"。 throw oneself into 是一个固定短语，字面意思是"把自己扔进..."，引申为"全身心投入某事"，强调非常热情和专注地开始做某事。