Usage patterns
本当に〈形容詞〉really/truly + adjective, for emphasis
This cake is really delicious.
本当にありがとうthank you so much / truly grateful
Thank you so much for helping me.
本当に〈事〉なのis it really true that ...? (seeking confirmation)
Expressions
本当にまあhow admirably; how wonderfully; how skillfully