In order to setup Gsuite on Hostinger you will need to have an active domain and Gsuite service purchased.
First of all, login to your Hostinger account, go to Home section, press Setup Gsuite and enter your domain name and again press Setup.
After you setup Gsuite, press Manage on your Gsuite and create Gsuite Admin account. For example: admin@your-domain-name.TLD
Then, login to your Gsuite admin area by pressing Go to Webmail or Login button and follow the setup on your Gsuite admin area.
After this step you will see pop up Verify your domain. Press on it and you will see your domain verification code.
Make sure to verify your domain ownership by adding TXT record with your verification code in your domain's DNS zone. See other verification methods here.
After that, you will need to wait for DNS propagation which can take up to 24 hours.
You are now able to use your Gsuite service and access your mailboxes by clicking the Go to Webmail menu: