You can embed videos in your post or page content. Here is an example from YouTube. Many other popular sites are supported. You can even upload your own video to WordPress. The theme makes the videos responsive so they show nicely on mobile devices.
Normally, an excerpt is shown on the short view of a post (when viewing multiple posts). The excerpt is either manually entered by you or automatically generated from the first few sentences of a post. Instead of showing the excerpt, you can show the first part of your actual post content (including formatting, images, etc.) and control where it breaks.
For example, you are reading the main post content right now (not an excerpt) and the “more” tag has been placed directly after this paragraph. As a result, on the short view, no more content is shown after this paragraph. Instead, a button for reading the rest of the content is shown. The user then clicks that to view the full post.