How can I edit a template and then use it later for a blog post?

I am finding getting started frustrating. I have no idea how to choose a template, edit it so the layout works for me and then save it as an accessible file, have access to it later so I can then use it for future blog posts. I have the Pressroom theme. Please guide me where to begin, this is so difficult. Thank you!


Will help you, are you a web designer? if you know any web designing software, like dreamweaver?