I need help with my header

Hello

I’m something of a neophyte to hosting my own wordpress site. I don’t know html but have managed to pick up clues here and there that allow me to understand how to do certain things. I am usually a quick learner.

I’m using the Twenty Eleven theme. I can’t afford to pay someone to design my website hence striking out into the confusing landscape that is html or is it css?

I would like to change the header on Twenty Eleven to my own brand logo but all the info I’ve picked up so far is confusing me. Frustrating because I’m keen to get the site live so that it can start earning me money – my business will depend on it.

Is there a clear cut way to go about this?