Email is often provided by your ISP (Internet Service Provider) eg BT, Talktalk, Sky etc. Other times you may have a Microsoft Outlook.com or gmail (Google) account.
Nearly all email providers allow you to access your email via the Internet browser, e.g. Edge, Chrome by logging onto your email account at e.g. BT.com or outlook.com etc.
This allows you to access your email from any computer that has Internet access - as long as you remember your email name and password! What password ??!!
Email programs (apps) such as Microsoft Outlook or Windows Mail are installed on your computer and are designed to download your email and store them and their attachements on your computer.
Email programs also allow checking of incoming messages with Anti-Virus programs, eg McAfee and they have a rich set of features to manage your email better - for example signatures, spell checking and email archiving.