Hello Jen,
Congratulations on your new MacBook Pro! I understand how important is to have your email account setup on your new computer. I found a couple of resources that I think might help.
You can check the Mail Setup Assistant for the server settings for common email providers. I recommend checking your email settings here first to verify they match what you have in the Mail application:
Mail Setup Assistant
https://www.apple.com/support/macosx/mailassistant/
If the Mail Setup Assistant does not provide settings for your email account, you can use the following article when contacting your email service provider to gather the necessary information to setup your account:
Configuring Mail for your email account
http://support.apple.com/kb/HT1277
If you are able to setup your account but messages are not being downloaded, I recommend reviewing the following article:
OS X Mail: Troubleshooting sending and receiving email messages
http://support.apple.com/kb/TS3276
Thank you for using Apple Support Communities.
Best,
Sheila M.