Pro has three main features in page building. The header, content, and footer builder. It also has some built in Theme Options that you can use to customize your site.
There is no specific way to start building a site with Pro but what I can suggest is for you to familiarize yourself with the options that you can find in the Theme Options area. You could see this in Pro > Theme Options. There you can set global settings like fonts, site width, stack, and etc.
Once you have explored and set options in the Theme Options area, you can then go check the Header builder. There, you can build the header area of your site. You can also assign a global header or assign a header to a specific page.
After that, you could check the Footer builder and create your custom footer which just like the header building, you can assign to a specific page or set it as the global footer.
You may check this video for an intro to Header and Footer Builder:
Note that things mentioned above are mostly likely going to be used globally throughout the site. After you have created those, you can then start building the pages using the Pro content builder.
It would be best to check out our knowledge base which contains a lots of helpful articles and should help you be familiar with the theme.
Hope this helps.