How to add my text to some pages?

You could place any HTML text to the Home, Products Listing or other pages by specifying the content in any custom block available in CMS > Custom Blocks section and then adding the block via CMS > Pages Layouts.

If you need to show custom block only for certain categories, manufactures, products etc. there is a number of Parameters you can use in custom block settings (CMS > Pages Layouts > click on 'tools' icon of the block):

item_id - for products, articles and ads
category_id - for any kind of categories
manf - for manufacturers
search_string - when a user is doing some search
article_id - to show block only for some articles

For example:
category_id=0,13,48

0 (top category), 13 and 48 are the categories where the block will be shown.