i just got an email from Apple ID Support saying my apple id was used in Moscow Russia. How do i know if this is legitimate?

As the other users says is quite difficult to image it's legitimate.

In case as we suspect is not, report the mail to Apple: Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support:

Report phishing attempts and other suspicious messages to Apple

To report a suspicious email, forward the message to Apple with complete header information. To forward the email: In macOS Mail, select the email and choose Forward As Attachment from the Message menu at the top of your computer screen.

These email addresses are monitored by Apple, but you might not receive a reply to your report.

• If you receive what you believe to be a phishing email that's designed to look like it’s from Apple, please send it to reportphishing@apple.com.
• To report spam or other suspicious emails that you receive in your iCloud.com, me.com, or mac.com Inbox, please send them to abuse@icloud.com.
• To report spam or other suspicious messages that you receive through iMessage, tap Report Junk under the message.

Quite possibly not. A genuine message from Apple would come from the apple.com domain and would address you by name, not your email address, nor 'Dear Customer' or similar. Either way, do not follow any links. If you want to check your account go directly to the Apple ID web page. You could change your password to be on the safe side - sign out of iCloud and iTunes on all your devices first to avoid problems.

Click here and check.

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