1. What does it mean?
가보자고 turns a suggestion to go or try into an enthusiastic rallying cry. People use it before a challenge, a new experience, a game, or a small everyday task when they want to build momentum.
Also written or said as gabojago
2. The nuance
It need not involve physically going somewhere. Tone can be sincerely encouraging or comically dramatic, and it is more casual than a formal proposal.
3. Examples
“처음 해보는 요리지만 가보자고.”
I've never cooked this before, but let's give it a go.
“자료 준비 끝났으니 발표 가보자고!”
The materials are ready—let's do this presentation!
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.