If your email is stored on the web, it's called 'webmail'. To access a webmail account, you get onto the internet, go to the website where your webmail is hosted and 'log in' or 'sign in' with your username and password.
You can also have an email account where your emails are stored on an internet-connected device like a desktop computer, laptop or tablet. This way, you'll access your email with special software usually called an 'email client'.