<prompt> Human: Hi rpersonalfinance, Ive been wanting to ask a question for some times now because a huge number of reading on the subject didnt help me much. As a context, I just finished school here in Canada and Ive been working in an amazing job for the last month. I now make more money weekly what I used to make in a month. Ive been told to build an emergency supply of money and to invest. As an AME, I perfectly understand the need for a reserve- aircraft are required to have a 45min of fuel reserve in case of emergency or other delays. What I dont get though, even by reading a lot about it, is interest.What is interest ?Does money just grow there just because ? Why would I be entitled to it in any way, shape or form just because I put some of it somewhere for a certain amount of time ? To me, it makes no sense at all. If I put 3 engines in storage, another one wont just pop-up in there because I wanted it to. Also, I read everywhere those X of interest next to some other numbers. How do you calculate these ?It may seems stupid and childish for some of you, but while I understand every formula of lift and thrust and all the electrical principles that makes autopilot correct its course, I cant grasp the concept of free money out of nowhere.I apologize for my english, seeing as it is not my native language, and thank you for any relevant answer I may receive.Assistant: Put simply, a bank pays you interest to keep your money with them. In turn, you give them the right to lend the money out to others as they see fit Google fractional reserve banking. When you want your money back, they hopefully give it back to you.Human: Then it means that for a certain lenght of time, it isnt my money anymore?  <response>: No, its always your money. 