It includes whatever you want to do with your investment. At least initially, it's not so much a matter of calculating numbers as of introspective soul-searching. Identifying your investment objectives means asking yourself, "Why do I want to invest?" Then you gradually ask yourself more and more specific questions to narrow down your goals. (For instance, if your answer is something very general like "To make money", then you may start to ask yourself, "How much money do I want?", "What will I want to use that money for?", "When will I want to use that money?", etc.) Of course, not all objectives are realistic, so identifying objectives can also involve whittling down plans that are too grandiose.
One thing that can be helpful is to first identify your financial objectives: that is, money you want to be able to have, and things you want to do with that money. Investment (in the sense of purchasing investment vehicles likes stocks or bonds) is only one way of achieving financial goals; other ways include working for a paycheck, starting your own business, etc. Once you identify your financial goals, you have a number of options for how to get that money, and you should consider how well suited each strategy is for each goal.
For instance, for a financial goal like paying relatively small short-term expenses (e.g., your electric bill), investing would probably not be the first choice for how to do that, because: a) there may be easier ways to achieve that goal (e.g., ask for a raise, eat out less); and b) the kinds of investment that could achieve that goal may not be the best use of your money (e.g., because they have lower returns).