Ideas have a snowball effect - if you start rolling a snowball, it grows larger and larger as more snow sticks to it. Most ideas start out small, but the more you think about them, the more they grow. You've probably heard the expression that genius is 1% inspiration and 99% perspiration. This is very true when it comes to story ideas. Most people could probably come up with an idea for a new invention, but not everyone will actually try to create the new product. Stories are like inventions in that there are plenty of ideas out there, but if you want to write a story, you have to be willing to work on it, to make it into something more than an idea.
I have always loved to daydream, and most of my stories become stories because I spend so much time exploring the possibilities of that idea, running different scenarios, and adding things to the story. But you don't have to love daydreaming to be a writer - you can also record your ideas and outline some story possibilities, or just start writing about something and see where it takes you. There is no set method that you have to follow - what's important is that if you want to be a writer, you write consistently even when you don't feel particularly "inspired." There is a perception that you're supposed to just wait for an idea to strike you. But you have to sing to be a good singer. You have to run to be a good runner. And, likewise, you have to write to be a good writer.
If you want to be a writer, the process of writing should be enjoyable. Sure, there will be times when you're frustrated with your writing or when you'll really struggle to crank out one sentence, but you should be able to say, in general, that you like writing. In most plays that I've been in, we spent 2-3 months rehearsing for a show that had only one or two performances. All that rehearsal just for 4 hours of glory. That's why it's important that you enjoy the process. I looked forward to shows, but I also had a ton of fun going to play rehearsal every day. While you may look forward to a specific writing goal, such as being published or sharing your finished work with your friends, it is important that you enjoy the process, because unlike being in a play, you don't have a commitment to anyone else, and the show won't go on without you.
Writing, like any other skill, takes practice, and for a lot of us, it involves writing when we don't really feel inspired. If you were in a band, in a play, or on a sports team, you would have regular practices, and you would probably have to practice a lot on your own, even on days when you didn't feel like it. This doesn't mean that you have to write every single day - it's up to you to decide how often you want to write. But whether it's every day, once a week, or even a few times a month, you should work on your writing consistently. Of course if you come up with a great idea, you should write it down and start exploring it right away, but you should also have a minimum amount of time that you plan to spend on your writing, whether you feel inspired or not.
Finally, keep in mind that all writing practice counts. If your team practiced very hard but lost a game, you would probably understand that all your practice time was not a waste, because you'd play better in your next game. The same is true with writing: when you write something that isn't very good, don't think for one minute that you've wasted your time on it. You're practicing, the same way you would practice anything else, and you will have to get through some not-so-good stories before you reach something brilliant.