You have the common notion of free will, which is "I can make decisions", and that is correct. But you probably also believe in cause and effect, and that every effect has a cause which produces it necessarily.
You can compare it to a vending machine. A vending machine also makes decisionsy albeit only very simple ones: if you press the coca cola button and haven't fed the machine enough money, it will decide not to give out a Coke; if you've thrown in enough money, it will give out a Coke and then, depending on how much money you've thrown in, it will make a decision whether it will give change, and if yes, how much change. All of these decisions are made autonomously by the machine, so you could say it is a somewhat free agent.
Now, you are no different. You can also make many different decisions; but you are not free in which decision you will make. For example, you think you have the choice of either staying seated in front of your computer right now, or to go to the fridge and get ice cream; OR, you could decide to jump out of the window of your tenth story appartment—or at least it seems to you that way. But in most cases, you can not make the decision to jump out of the window, unless the motivations (causes) are sufficiently strong to overpower all the other motivations (SI, comfort seeking, etc).
If I press you on it, you couldn't even define what you mean by free will, aside from saying you can make choices—which doesn't give you any more freedom than a (very complex) vending machine.
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And if you wanted to demonstrate to me now, out of defiance, that you actually CAN decide to jump out of the window, well: then my challenging you and your anger at me were the cause of you jumping out of the window
. No way to escape it