Hi @dishasharma ,
Email Delivery:
The Email Delivery activity is used to send the communication either single send email and sent just once, or it can be a recurring email.
If the Workflow which you use don't have a scheduler activity, then the Email Delivery activity will run only once(ie, the Delivery will get created for 1st run and wont be enabled to run again for next run) and if the same have the scheduler activity , then it will behave as a Reccurring Delivery(ie, it can be used to send delivery multiple times in same WF).
Delivery activity:
It would have multiple options to select, as shown below

This can be used to send the email via a delivery Template or using a script to create a copy of delivery template and so on...
We can use it based on the Requirement given to us.
https://experienceleague.adobe.com/docs/campaign-classic/using/automating-with-workflows/action-activities/delivery.html?lang=en
https://experienceleague.adobe.com/docs/campaign-standard/using/managing-processes-and-data/channel-activities/email-delivery.html
Regards,
Pravallika.