"Have a go" is an English expression that indicates that someone is going to make an attempt at accomplishing something. It is often said when others have tried to do the same thing but have failed in their attempts. There is a connotation tied to this phrase that implies that the person doing the trying is unlikely to have any success at the feat that he or she is attempting. Many phrases are similar to this one, including "give it a go" and "have a go at it."
Idioms are short phrases or expressions that often mean something quite different than what the literal definitions of the words they include might indicate. This is because the phrases gain their meanings from the way they are used in the culture. These idiomatic expressions are useful to speakers because they often provide shorter, more folksy ways of saying things that might be laborious to describe otherwise. One such phrase that is used often by people about to try something is the expression "have a go."
There are many occasions which might demand the usage of this phrase. It often comes when a person is just one of many people who have tried to accomplish something. The implication the phrase carries in this context is that this feat has bedeviled just about everyone else, but still the person in question is going to take a stab at whatever it might be. As an example, someone might say, "Well, nobody can seem to open that bottle, so I guess I'll have a go."
It is common for this phrase to be used when the person making the attempt is unlikely to achieve his or her goal. Usage of the phrase in this manner suggests that the person will valiantly try to get the thing done even if the odds seem stacked against him or her. For example, consider the sentence, "This math problem seems just about impossible, but I'm going to do my best and have a go anyway."
In certain circumstances, slight variations of this phrase might be used. One very similar expression is the phrase "give it a go," which has basically the same meaning. The phrase is often elongated just a bit when someone says that he or she will "have a go at it." Regardless of what version of the phrase is used, the basic gist of it is that someone is going to make an attempt or take a turn at trying something.