All templates use the K2 Component as their basic content manager. Here are some basic quidelines of how to install and set it up correctly. For more details on each template's specific setup, please advise its documentation, Visual Walkthrough and the demo site or Quickstart package.

1. Install K2 Component. Go to the Extensions Manager and install the latest version of the K2 component. Download it on getk2.org.
2. Setting up K2 General parameters. After a success message, navigate to Components → K2 and from the toolbar on the top right corner, select the Parameters Button. This will open a modal window with the general K2 parameters you have to set up according to your needs. One of the parameters that needs to be set before any item addition are the Image sizes. Here are the available sizes for all K2 views and modules: XS, S, M, L, XL, category image, user image, commenter image. Advise each template's documentation located in this section or the Quickstart package for the recommended sizes.
3. Setting up K2 Categories. Create your category tree in K2 Categories, which will be according to the structure of your site. Set the parameters in your categories, advise the Visual Walkthrough of each template or the Quickstart package, in order to view the resulting pages you see at the template's demo site. It is recommended to keep the parameters in one root category and set all others to inherit from that one. In most of our Quickstart packages the setup categories are marked with "DO NOT DELETE" on their name for better reference. The parameters differ between templates according to structure and features.
4. Adding K2 Items. After you have set all parameters up, you are ready to add K2 Items. According to the needs of each template, several K2 Item elements are used. These elements include Image, Image Gallery, Media, Extra Fields, Attachments. On each template's documentation, Visual Walkthrough or the Demo site, there is a more detailed reference of the ones being used on each template. 
5. Setting up K2 menu items. Your available options are between views of: Item, Category/Categories, Latest items by tag, Latest items by user, Tags list, Author list. The item view gets its parameters from the category it belongs. The category also gets its parameters from the category, while there is the option to multiselect categories and set the list parameters for them. You can also override the ordering of the Category parameters through the menu item. The author and tag lists get their parameters from K2 general parameters. The latest from user/category views are the only menu item views that have their parameters here instead of a category or the general K2 parameters.

Please note that all the above steps should NOT be followed if the Quickstart package is used. All setup has already been made according to each template and should work as a guide for your own customization.

For more information about K2 functionality, visit getk2.org.