let=让，us=我们 let's 让我们。。。吧 Let's go see a movie.让我们去看电影吧 Let's eat.让我们吃吧/开动吧 Let's take better care of our environment.让我们更好的保护我们的环境 but usually ,in spoken chinese,when we say something like"let's blahblahblah" ，we just drop “让我们” Let's go see a movie.去看电影吧 Let's eat.吃吧/开动吧 you can't dump让我们in the 3rd sentence you gave,b/c it's a formal way to say it.

Chinese people can correct me if I'm wrong, but I think people sometimes do this by adding 吧 to the end of the sentence. For example, when a group of people are eating a meal together and it's time to leave, I've often heard someone say: 走吧？(Let's go!) There are probably other ways to do this that I don't know about. I think a lot of times the meaning will depend on the context and there may not be a single fixed expression that always means "Let's..." 中国朋友们，我说得对吗？

让我们＝let us If I suggest something ,then I will say "我建议去做xxxxx, 好不好？" 例如： 我建议下午去购物，好不好？

the chinese character 吧also means inqiuring or wondering if you agree to the plan or suggestion.for example,let's go,which meant chinese 走吧，if here 吧 is stripped off,the words's tone will get high and it's meaning will get compulsory.

"let's" means "让". Sometimes, we don't need say it in some sentences. Let's go see a movie. 看电影去吧. Let's eat. 吃饭去 or 吃饭去吧. Let's take better care of our environment. 让(我们)更好的保护我们的环境. "吧" doesn't has specifical meaning here, it is just a grammatical role. If I didn't put "吧" in those sentence, they would be so weird.