Select the appropriate section for information on adding your content to ArcGIS Online:
Uploading maps, layers, and tools
Best practices for tagging your items
To upload maps, layers, and tools:
.

Once your item is uploaded, it appears in your content workspace and you can edit the properties and share it.
.

Once your service is referenced in ArcGIS Online, it appears in your content workspace and you can edit the properties and share it.
Tags are words or short phrases that describe your item. The most useful tags are keywords that users might enter in a search string when looking for your item and are not already contained in the title (titles are queried by search engines, including ArcGIS Online, so it is not necessary to repeat title terms in your tags). For example, it you have a map documented with the title “Denver hydrology”, you might want to tag it with the following terms: water, stormwater, wastewater, Colorado. Remember to separate terms with commas. Federal lands is considered one tag while Federal, land is considered two tags.
After you’ve added an item to ArcGIS Online, you can make the following modifications: edit the property fields, change the sharing properties (the setting is private by default), delete it from the system, move it to a different folder on your workspace, and, if it is a file, update the version.
You make these changes through the item properties page. From your content workspace, click the title of the item whose properties you want to modify.
Click the edit button to open the edit mode for the item properties page.
You can edit the text for the following fields: title (1), tags (2), credits (3), summary (4), description (5), and access and use constraints (6). To change the extent, click the Set Extent button (7) and either enter numerical values or use the map navigation tools to redraw the extent. TIP: Draw extent uses the extent of the box you draw on the Extent screen, not the extent of the map. When you have finished making edits, click the Save button (8).
Click the Update button to update a map, layer, or tool file with a new version from your computer.
Browse to the updated file on your computer (1), choose whether you want to preserve the item fields you have on ArcGIS Online (which you might have edited) or upload the fields from the item file (2), then click the Update Item button (3).
You can add a thumbnail to your item properties or you can update an existing thumbnail. To add or update a thumbnail:
TIPS: