If you decide to do something, you choose to do it, usually after you have thought carefully about the other possibilities.

If a person or group of people decides something, they choose what something should be like or how a particular problem should be solved.

If an event or fact decides something, it makes it certain that a particular choice will be made or that there will be a particular result.

If you decide that something is true, you form that opinion about it after considering the facts.

If something decides you to do something, it is the reason that causes you to choose to do it.