It is also possible to get one-on-one help online. You will get explanations and sometimes a written answer too. Still, the charge is per minute so you have to watch out. You have to be well organized to make the most out of the session.
While the first two options can be helpful for solving problems and answering questions in different academic disciplines like math, the natural sciences and economics, they are not particularly useful when you have to write an essay in history, literature or philosophy, a research paper or a lab report. In such cases, you will need a custom writing service. In this case, a professional writer will do the research for you and write the required piece from scratch.