You are probably a Joomla newbie, so don't be so hard on yourself :)

In order for any content in Joomla to display, you need to have menu items pointing to components or other content sources. So, in the case of K2, you simply need to create some menu items that point to one or more K2 categories, tags, users and so on.

Use reCaptcha v2 keys and make sure you select "v2" in the K2 settings as well. v1 is deprecated and Google's reCaptcha will not issue v1 compatible keys.

Create menu items point to K2 categories. Simple as that. If you need to display items in a sidebar, use the "K2 Content" module to fetch items in various ways.

Gotta be more specific Liam...