Hi, Cindy,
I am still fairly new but I will attempt to help with what I have learned so far.

To your question 2. What is Streamlining Testing

My attempt to clarify,

For example, when you reference an outside page (whether an affiliate link or another website), instead, you can send the visitor to the review page on your site, rather than sending them directly to the outside page.

This is called internal linking and Kyle refers to it as centralizing your offer page.

Kyle mentions these other advantages:

Aside from improving your Google ranking, doing this allows you to manage a single page, in having to manage only one page, you are streamlining testing - you only have one page to test

3, A product having an affiliate program

A product offering is done by placing links (provided by affiliate programs that you are a member of) on your pages to promote their products for sale as a member of the said affiliate program.

Maximizing these is a very broad topic. In my short time here, I find that I strive, when possible, to make sure that these are opened in a new page so my page is not gone from their browser when they click on the link.

I am also experimenting with broader offering pages (whole product lines versus single products) with compelling pictures and a clear description. As an example, rather than a blender, I will try to cover Kitchen Products (most affiliate programs will provide links to do so).

I'm sure some of our more experienced members will chime in too, in the meantime, I hope the above is helpful.

I can only really answer the first part of your question.
On the post you are trying to edit, select the text you want you link to appear on, click on the chain link icon (see attached image) from there click on the gear icon and a new box will appear. You will have the option to type in a link or chose one of your other posts. This is how you can link to content within your own site. Hope this helps.