Play the video below if you would prefer to see how to do this.
Find the Activity (see Find content in Find Learning or Find content in Content Manager if you're unsure how to do this) you would like to assign an Email Reminder to and go into its administration area.
From the Common Tasks tab of the Activity, click Set reminder emails.
Alternatively, you can click on the Email Reminders tab on the left-hand side.
If any Email Reminders have already been created, they will show up here.
To create a new one, simply select New Email (you will not need to click on this button if you have used the link in the Common Tasks area). 
You will now be presented with a 3-step wizard.
Step 1
Add a subject for your email to the Subject line. Using the Custom fields on the right-hand side to insert personal information, create an email welcoming Users to the site. Simply click on the link of the Custom Field to add it.
In this example, which is confirming a User's registration onto an Activity, the email could be worded as follows:
Click on the Send Test Email to check the formatting. Please note that the test email will go to your email address and it will be addressed to you, as you are logged in as an Administrator, and the set password link won't work if clicked on as it is a test email.
Click on Next once you have checked your email and are happy with it.
Step 2
This step allows you to set who will receive the email. If you want the Email Reminder to go to everyone, you don’t have to set up a rule, so you can skip this step by clicking Next.
Otherwise, if the email will be targeting specific Users, click on the Click to add link.
Search for the relevant Groups (or tick the boxes next to the Categories if you chose this in the above step). In this example, the email is for the ‘Bank of Unicorn Limited’, so we’ll tick that.
Click on Next.
Step 3
The final step allows you to set up how often to send out the email. If we wanted to send this email to go out at a future date, we would select Start running on and enter the date, as shown below.
You might also notice from the above screenshot that there is an option not to send the email and save it as a Draft instead.
As this example is an email to confirm a registration, we want it to go out On registration, to Start running now and send to the Registered User, as shown in the screenshot below.
Click Finish to complete. You will be returned to the Email Reminders tab where you can edit, cancel or delete the Email Reminder.
Don't forget, you can set up multiple Email Reminders for different purposes. For example, to reminder Users of Due Dates, congratulate them on completing the learning, or even just to send them information on a once-only basis.