Manipulating how posts are displayed

I am modifying a wordpress blog for my new project.

I have been trying for house, looking through the documentation as well as looking through themes.

I need to figure out a way to display a specific post. So if I have a post ID number, is there a function to pass that value to it and it will display that post?

Also, is there a way to display all the posts from within a specific category?

Any help will be very appreciated, I am new to wordpress programming, but I am experienced in PHP and everything.

Please point me in the right direction. Thanks!