If you are talking about this ba 吧, it has many usages. It is normally used to indicate a strong urge or suggestion, for example:

走吧
Zou3 ba
Let’s go

快点吃吧
Kuai4 dian3 chi1 ba
Eat quickly

赶快洗洗手吃饭吧
Gan3kuai4 xi3shou3 chi1fan4 ba
Wash your hands and have lunch

“ba” could also be used to indicate doubt or uncertainty. For example:

她是你的朋友吧?
Ta1 shi4 ni3de peng2you ba?
Is she your friend?

The above sentence indicates that you are not 100% certain whether someone is a friend of a person you’re talking to or not. In such a situation you might put “ba” instead of “ma” at the end of the sentence to make it a question.

“ba” could also be used to indicate agreement or acknowledgment. For example,

好吧
Hao3ba
Okay/alright

If 吧 (ba) appears in the middle of the sentence, then it indicates ‘a pause’.

Am I right Benny?

Lee Kong