Use your @g.cs****com Google Workspace login to manage these!
https://www.partneradvantage.goog/ – partner program – mostly useless, but training is accessible from here, all certification, all corporate functions; if you are already logged into a different gmail account – best to use this with incognito or in separate browser
https://channelservices.cloud.google.com/ – GSuite reseller console – create a new customer, customer billing information;
https://gsuite.google.com/products/admin/ – single tenant admin site; have to have a admin at the tenant level to use this site
IF YOU want add a google account to your customer, get the transfer code: https://cssi.us/g-suite-reseller-transfer/