Creating headers

Hello

I am fairly new to WP and need some advice/assistance.

My site is https://www.vickiclarkephotography.com

I would like to do something with my header, as at the moment its just the name of my site in the standard font of the theme.

I have created a very basic header in photoshop (im new to this too)
I have created it with a transparent background. I then loaded it up to WP, but the background became black, and you could not see my header.

Am I doing something blatantly obviously wrong?

I have tried the background in white too and this has not worked either.

Can anyone help?

Thanks
Vicki