Hi there!
Before you can share a layer package, there are two options on where you want to save your file. Make sure you have chosen the "save package to file" and not the first one because that means you're going to upload the layer to your AGOL account as you were saying.
Second, tags, description and summary are required fields in creating layer package. Just put any meaningful words to describe your file and that would be good to go.
You may want to check attached images for reference.
[ATTACH=CONFIG]31967[/ATTACH][ATTACH=CONFIG]31968[/ATTACH]