I am new to video editing. I have been using iMovie and there is a preset video intro with a space-theme that I like but i want to edit the intro itself which the iMovie software won't allow me to do. What steps can I take to create the intro myself?
First up you'll have to upgrade to a different Video Editing program that has more support for the custom effects that you'll need to create an intro. For professional-looking video intros, I recommend using Adobe After Effects. Premiere Pro, Sony Vegas Pro and Pinnacle Studio are also viable options.
Since you're new to video editing, I recommend looking for some tutorials on what you're trying to achieve. I found this tutorial on YouTube which seems to fit your description:
Take what you learned from watching tutorials, and use it to create the intro you that suits you.