The phrase "get the picture" is an idiom that means to fully understand the meaning or the main point of something. "Get the message" and "get the meaning" are similar phrases that mean the same thing. All of these are generally used as ways of ascertaining if a person comprehends a situation or conversation, although the phrase might be more implied than stated or asked outright.
It can be used as a question, as in, "Do you get the picture, or do I have to tell you again?" or as a statement, such as "Yes, I get the picture, you can stop explaining." Alternatively, the speaker may ask someone who appears to be confused about the main point or unable to follow the logic behind the speaker's words, "You're not getting the picture, are you?" In that instance, the speaker may realize that he or she has not been communicating the ideas effectively, and may choose to try and "paint a different picture" for the listener to "get," or understand.
The idiom can also be used in situations where the meaning of events or actions needs to be interpreted. For example, an employee may be able to pick up on and interpret the subtle actions and moods of his boss well enough to figure out that he is about to be promoted, or fired, at the next business meeting. Similarly, a child may realize in late November that his parents have not been buying him as many toys as usual and appear to be spending less money, and deduce that they are probably saving for a large Christmas gift. In both cases, the individuals have successfully gotten the picture despite the best efforts of the employee's boss and the child's parents at hiding the situation.
In instances where one person may want to hint at a situation without directly stating anything, he or she may allude to something and then trust that the listener understands the meaning. For instance, a person reluctant to break the news to a friend about a cheating spouse may hint that the spouse has been staying at work later recently and seems to be acting distant, hoping that the friend will get the picture and not require a full explanation of the unpleasant circumstances. In another example, a nervous man might hint to the woman he is interested in that he likes her, in the hopes she will get the picture and make the first move.