To install X, go to your wordpress dashboard and go to Appearance > Themes > Add Theme > Upload Theme and pick the X theme from where you downloaded it. Then activate it.
There are some tutorials here on YouTube that you can check out: https://www.youtube.com/channel/UCAgQdxFimOzBGEpw2pgrv7A
You can check out the Knowledge Base here:
Here are some more help articles:
I would browse the knowledge base and read up on that and check out the youtube tutorials.