To start, login to cPanel. Under the domains section, click "zone editor".
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On the next page, you'll see a list of your domains. Off to the side are actions you can take. Choose the domain you wish to add the a record to and click "+A Record".
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A popup window will appear, enter the name and then the IP you wish to connect it to. Click "add an A Record".
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A green popup will appear saying "you've successfully created an A record". That's it! You've successfully created an A record!