Hi,
To apply different paragraph styles within a same text frame you need to have different paragraphs first(by pressing Enter?) which means your header, page number, desription in the text frame should be in different paragraphs.
Applying a different paragraph style should then be easy.
1. Click in a paragraph, or select all or part of the paragraphs to which you want to apply the style.
2. Do one of the following:
a. Click the paragraph style name in the Paragraph Styles panel.
b. Select the paragraph style name from the menu in the Control panel.
c. Press the keyboard shortcut you assigned to the style. (Make sure that Num Lock is on.)
3. If any unwanted formatting remains in the text, choose Clear Overrides from the Paragraph Styles panel.
Otherwise if you do not wish to create separate paragraphs but still apply different styles, try creating character styles instead.
You can read more about styles here Apply paragraph and character text styles in Adobe InDesign
-Aman