I would like to put an Ad Tag in my blog

I am trying to put an Ad Tag on my blog. The company gave me a bunch of script (starting with <script language) and told me to “paste the following script into any of your web pages”

Can someone tell me how to do this?

I have little computer knowledge, my site is set up with a template and I fiddled around with something like this last night and ended up with a white website!

Thanks,
Alicia