I want to use wp to create a blogging site. I have no experience with it. I have a few questions about wp: `1. Can any theme be changed (if not on the dash then in the code)? 2. Is there a good source and a bad one to get a free theme from? 3. I heard when wp updates the program it can "break" a site's theme. What does that mean? What should I do to prevent the breaking from happening? 4. Do you recommend any theme? 5. If I create pop up windows to ask for their email does that harm wp in any way?
I'm glad to hear that you're interested in blogging. It's a great way to share your mind with the world.
Wordpress actually has two different websites/types. The first is Wordpress.com and the other is Wordpress.org. Here's the differences:
Wordpress.com hosts your website directly on their servers, so all you need to get started is to setup an account. It has a free version which is limited in it's features, but you can upgrade if you want more options.
Wordpress.org allows you to download the Wordpress software for free and put it on your own server. To do this, you would need to purchase hosting from a website such as Hostgator.com. It would be slightly more expensive going this route, but Wordpress.org has many more options. This is what I use for each of my websites.
Now to answer your questions:
2) Both Wordpress.com and Wordpress.org offer many free themes to choose from. I would recommend that you start there, since they are normally trustworthy. When downloading free themes from another website, be careful because some themes might have malicious code tied to them. You can find many bloggers who make lists of good free themes. Just google "Best Free Wordpress Themes".
3) I've never encountered one of my themes breaking when I updated Wordpress. I have experienced plugins (which add special functions to your website) that will break during an update if they aren't written properly. But Wordpress.org offers so many plugins that you can usually find a working alternative.
4) A good starter theme comes with Wordpress. I believe the current one is called Twenty Thirteen. You can also check the themes available on the Wordpress websites. They offer many great choices. It really comes down to your topic and how you want your website to look and feel.
5) Creating popup windows won't break your website. I personally don't like popups and I think that they will scare off readers. But that's my opinion. I prefer using subscription boxes that will slide up from the bottom. There's a really good plugin that will do this in Wordpress: https://wordpress.org/plugins/scroll-triggered-boxes/
I would recommend that you visit the Wordpress.com and Wordpress.org and decide which would be best for you. Search through their Plugins and Themes sections and can find ones that are a good fit for you.
Let me know if I can be any further assistance.