Mark, you only have to pay if you are 100% satisfied and you don't have to subscribe if you are not interested. That is optional.
Re your problem, You don't need a Gmail password ***** update app. But it sounds like your Mac is asking for the Apple ID password. Apple ID would be your gmail address, but the password ***** ***** from gmail password.
If you don't remember the password, then you have to reset the password. You can reset it from here (go to this website from your computer) --> https://iforgot.apple.com/
Go to the above website. Use the "Get an Email" method to reset the Apple ID. Apple will send the reset instructions to the recovery email you setup with your Apple ID. It would be your email registered with Apple, like Gmail. Open your email and you will see the email from Apple. Open it and follow the instructions to reset the password.
If that didn't work, then go to this site again --> https://iforgot.apple.com/
This time use the "Answer Security Questions" and answer the security questions there to reset your password. Then use that password ***** update your apps.
Please let me know if that didn't work, so I will continue to help you