Then let us start the test process step-by-step.
Notes: we will create a new Task by copy a already one.
In this case, I will use Task(guid'FA163EEF-573D-1EE5-9686-8E98F573FCA3') as a create sample.
Step1. We use get method receive the details of Task(guid'FA163EEF-573D-1EE5-9686-8E98F573FCA3').
HTTP method: GET
URI:/sap/opu/odata/sap/CRM_ODATA/TaskCollection(guid'FA163EEF-573D-1EE5-9686-8E98F573FCA3')
Action: F8
Result: You will get a HTTP Respond, show all the details of Task(guid'FA163EEF-573D-1EE5-9686-8E98F573FCA3').

Step2. Click on [Use as Request], trans the HTTP Response to HTTP Request.

Step3. For creating a new Task, we need change the values in the request body as required.
(1)One action is required.
field <d:guid> need change to as below. For <d:guid> is the key of a Task and it's format is '00000000-0000-0000-0000-000000000000', and can be generated auto when a Task is created.
<d:guid>00000000-0000-0000-0000-000000000000</d:guid>
(2) In this case I will change some other fields for the new Task, I will change discription.
Step4: Change the URI to URI:/sap/opu/odata/sap/CRM_ODATA/TaskCollection.
For when create a new Task, we do not need a guid in URI.
Step5:
Set HTTP method: POST

Step6:
Click F8.
Result: If the HTTP Respond code is 201, then you create it successfully.
Result:
HTTP respond code: 201
New Task(guid'FA163EEF-573D-1ED5-968A-741ED0990906') and with<d:description>Sara test for create demo</d:description> generated.

Step7:
Do double check in DB.
Step8:
Do double check in Webpage.