Some people swear by outlining. Others hate it.
Should you have a plan if you’re writing a novel that you’d like to publish someday? Probably’d be a good idea.
Your outline can change. For some reason, some people think that if you make an outline, you, by all means have to abide by your outline. Your outline mostly is there to tell you what needs to happen at the beginning and what needs to happen at the end and how your characters get to said ending.
Some things, you’re going to realize, just don’t add up and don’t make sense. You add that in when you’re writing and it will begin to make sense.