See explanation below.
Explanation
1. Navigate to the Exchange Admin Center
2. Navigate to Compliance management > Retention tags, and then click Add +
3. Select the Applied automatically to entire mailbox (default) option.
4. The New retention tag page title and options will vary depending on the type of tag you selected. Complete the following fields:
Name: Enter a name for the retention tag.
Retention action: Select Delete and Allow Recovery option.
Retention period: Select When the item reaches the following age (in days) option.
Comment: User this optional field to enter any administrative notes or comments. The field isn't displayed to users.
5. Navigate to Compliance management > Retention policies, and then click Add +
6. In New Retention Policy, complete the following fields:
Name: Enter a name for the retention policy.
Retention tags: Click Add + to select the tags you want to add to this retention policy.
After you create a retention policy, you must apply it.
1. Navigate to Recipients > Mailboxes.
2. In the list view, select the mailbox to which you want to apply the retention policy, and then click Edit.
3. In User Mailbox, click Mailbox features.
4. In the Retention policy list, select the policy you want to apply to the mailbox, and then click Save.
Reference:
https://docs.microsoft.com/en-us/exchange/security-and-compliance/messaging-records-management/create-a-re
https://docs.microsoft.com/en-us/exchange/security-and-compliance/messaging-records-management/apply-reten

Explanation
https://docs.microsoft.com/en-us/azure-advanced-threat-protection/workspace-portal

See explanation below.
Explanation
Creating Office 356 labels is a two-step process. The first step is to create the actual label which includes the name, description, retention policy, and classifying the content as a record. Once this is completed, the second step requires the deployment of a label using a labelling policy which specifies the specific location to publish and applying the label automatically.
To create an Office 365 label, following these steps:
1. Open Security and Compliance Centre;
2. Click on Classifications;
3. Click on Labels;
4. The label will require configuration including: name your label (Name), add a description for the admins ( Description for Admins), add a description for the users (Description for Users);
5. Click Next once the configuration is completed;
6. Click Label Settings on the left-hand side menu;
7. The Label Settings will need to be configured. On this screen, you can toggle the Retention switch to either
"on" or "off". If you choose "on", then you can answer the question "When this label is applied to content" with one of two options. The first option is to . From the pick boxes, you can choose the length of retention and upon the end of the retention, the action that will take place. The three actions are to delete the data, trigger an approval flow for review, or nothing can be actioned. The second option is to not retain the data after a specified amount of time or based on the age of the data; and
8. The label has now been created.
To create a label policy, follow these steps:
1. Open Security and Compliance Centre
2. Click on Data Governance, Retention
3. Choose Label Policies box at the top of the screen; and
4. There are now two options. The first is to . If your organization wants its end users to apply the label manually, then this is the option you would choose. Note that this is location based. The second option is to Auto-apply Labels. With Auto-apply, you would have the ability to automatically apply a label when it meets the specified criteria.
References:
https://www.maadarani.com/office-365-classification-and-retention-labels/

Explanation
Find and export a user's personal data to help you respond to data subject requests for the General Data Protection Regulation (GDPR).
https://learn.microsoft.com/en-us/microsoft-365/compliance/microsoft-365-compliance-center?view=o365-world