How, exactly, do I place an ad on my blog?

[MrD]

Please don't tell me that trying to do affiliate marketing is premature for me at this point; I already suspect that, but I want to try anyway.

I have a fairly widely-read blog, and I need to make a little money, but I am probably the most computer-ignorant adult in the Western hemisphere. I've been accepted by several affiliate marketing programs, and have wonderful ads available, but I don't understand how to place them on my blog. The instructions, from the marketers as well as from blogspot.com, assume that one knows more computerese than I know.

Can someone please, in pure, SIMPLE, step-by-step English, tell me how to place ads on my blog? And no, I do NOT intend to overload my blog with ads.
@Jake: Thanks so much for your response. I'm not using Wordpress; I'm on blogspot.com.