Detecting if page is a ‘post page’?

I am a newbie to PHP but I have a programming background.

I am working on modifying a plugin and I need to detect if a page is a ‘post page’ or, more clearly, if the page is the main blog page.

My concern is that a site’s home page may not be the blog page, since we can set the home page to any other page, and the blog page is the page that I want to work with.

is_home() will not work if this is the case, right?

I hope that makes sense?