Elgato Game Capture HD has a simple yet powerful editor, which is described in this article:
How do I edit an Elgato Game Capture HD video?
Once you split your recording into smaller segments, it's easy to share one or more of them.
Split Segment at Playhead
To split a video segment into two smaller segments, you can use the Split Segment At Playhead command.
Move the playhead to the point where you want the split to happen.
Then, use the button with an icon on a pair of scissors on it to split it.
Next, move the playhead to the end of the section you want to save, and then use the Split Segment At Playhead command again.
New Video from Timeline Selection
To share a particular selection, first click on it until it turns blue.
Then, right click on it, and select New Video from Timeline Selection.
A new clip will be created in your Elgato Game Capture HD library, that you can then share to YouTube or other sources.