How to add advertising to a blog

I’ve been clicking on every which button for the last hour or so, trying to find the right place to paste the code (for a banner advertisement) which the Amazon Associates programme supplied me with, and I just can’t do it. I tried adding it to my sidebar thingumajig, but it’s just a really long text link to the advertisement now, which opens in a separate page.

You’re going to have to speak slowly – I have no prior knowledge of all of these terms like ‘code’ and what to do with them. I’m not even sure I should be allowed to use the internet, but here I am and I need some help quick before I accidentally blow something up.

I guess I’m using the newest version of WordPress. And I promise I’m not this slow in real life.

Help very, very gratefully received!
Lola