Understanding the ready templates(Themes) for web applications

now I want to build a web application with firebase, when I made some search about styles I found a (ready template) like this from ThemeForest website, but I don't understand it enough.

my questions are:

1. can I bind these templates with my firebase database and/or firebase storage.
2. can I consider these templates instead of a web designer, in other words, it offers me just the structure and style of pages then I can customize it as I want.
3. what should I know for customizing it if this option is available.

finally, it will be great if someone gives me more explanation about a (ready template) and some recommendations whether these templates are helpful and how far it can help me.

thank you very much.