Step-by-step:

1. Open the Application site (See Part One: How to create the app catalog site for SharePoint online O365)

2. Select the “Apps for SharePoint” hyperlink on the left pane… Select the “Upload” button

3. Browse to the application on the local server… Click the “Open” button

4. Click the “Office 365 Settings” icon… Select “Add an app” from the menu

Click on the App… Select the “Trust It” button… Wait for the app to upload

5. Clicking on the Homesite, you will see the App menu displayed on the left pane

You have successfully uploaded an application from the local server to SharePoint Online.

To learn how to purchase an application from the SharePoint Store, see Part Three:
Store for SharePoint Online