Help, please! I am new to WordPress and lost

I am new to WordPress and I am in need of some help. I really like the simplicity of this template which is loaded here: http://frugallythrifty.com/ , but I have a custom header that I made already to go on it and haven’t the slightest clue how to add it. Can any of you please help me to get this done?

Thank you all so much for your help in advance,
Kristi