You'll get the Skype Integration settings in Settings > Setup > Skype Integration.
You've to integrate Microsoft Graph API to sync with Skype. Please follow the steps below to integrate:
Go to the Microsoft Azure Portal and click on Azure Active Directory. If it's not available, check on More services.
Click on App registrations from left menu the click New registration.
After that, you'll get a form like this. Fill up as below. In Redirect URI, you should add this url https://yourdomain.com/index.php/skype_integration_settings/save_access_token. You'll find this in your integration setting. Finally click on Register button.
Now, you'll get the Overview page. Copy Client ID from there and add to integration setting.
Click on API permissions from left menu. Then click on Add a permission.
Click on Microsoft Graph.
Click on Delegeted permissions.
Search offline_access and click on the checkbox.
Search Calendars.ReadWrite and click on the checkbox.
Finally, click on Add permissions button.
Click on Certificates & secrets from left menu. Then click on New client secret.
Fill up the form like below and click on Add button.
After that, you'll get the Client secret.
Add this Client secret also to the integration settings and click on Save & authorize.
On authorization, you'll get a page like this. Click on Yes button.
On retrieving from API access, please make sure that, status of Skype Integration is showing Authorized.
That's all! You've successfully integrate with your Microsoft Outlook Calendar. Now you can create meeting with the integrated Graph API.