ぞ emphasizes determination or certainty
Japanese
行くぞ!
English
We'll go!
Japanese
勝つぞ!
English
We'll win with this!
Japanese
負けないぞ!
English
I won't lose!
ぞ indicates inviting or encouraging in dialect
Japanese
一緒に食べようぞ!
English
Let's eat together!
Japanese
遊びに行こうぞ!
English
Let's go out and play tomorrow!