There are a couple of ways to delete emails.

It depends whether you are inside the email or if you are in your inbox and whether you are deleting one or more.

1) If you are inside the email, click the three dots and then click DELETE THIS MESSAGE.

If you are in your inbox, you can easily delete one or more emails without needing to open them.

1) Click the box to the LEFT of the emails you want to delete

2) Click the Rubbish bin from the top row above your emails