First of all, you need to get your Gmail SMTP credentials that can be used while integrating Gmail SMTP
Log in to your Google account with your login credentials.
Turn on "2-Step Verification" for your account
Create App password
Please go to link https://myaccount.google.com/ and click to menu "Security" then click to "App passwords" row in "Signing in to Google" section
Select options like image below
After clicking to "Generate" button, please copy your app password in the popup displayed
If you love LayoutHub, could you consider posting an review? That would be awesome and really help us to grow our business, here is the link.