How can you customize the header?

You can do this simply by clicking on 
Design-Page Elements-Header-Edit(Configure) Header!
Voilae

How do you moderate comments?

Firstly you need to set the option when creating your blog. This is the path: Settings-Comments-Comment Moderation


Now you can manipulate it: When clicking on Comments you will get an option for Moderation (Awaiting Moderation)

How do you post videos, slideshows, pictures?

You simply go to New Post- click on body of the message-now you can see the Toolbar above.

 Click on the on of the icons you require: Insert Image, Insert a video...

Creating a Blog

It's easy peasy lemon squeezy!

This link might be of a great help to pure beginners:
Where do I start? Blogging Basics, by Melanie Nelson and Karen Lewis
www.bloggingbasics101.com/how-do-i-start-a-blog