Different Sidebars for Different Pages?

I’m very new to WordPress, and I’m working with a custom template I uploaded. I have two questions:

1. There are sidebar “widgets” imbedded in the code of the template. Some of them are active and some seem to be placeholders. For example, there is a sidebar that says it is a placeholder for an Aside or for ads. However, when I create a sidebar page, it doesn’t show up anywhere on the sidebars of the page.

How do I activate those placeholder sidebars?

2. Is it possible to have different sidebars on different pages? I like all the sidebars on pages I’ll use to blog, but not necessarily on other static pages?

I should mention that my knowledge of coding is virtually nil.