Hi! What exactly is your scenario? Do you have users and data to migrated from on premises then to run cloud only or just start from scratch? What exactly do you need help with? Have you created a tenant? How to configure your tenant is up to you depending on needs etc.. But as a start you should:
Create a tenant
Add your custom domain - under setup - domains..you need to either let Office 365 host the DNS for your domain or enter the DNS records in the DNS you have today for the domain! Either way you need access to the dns.. Decide where to get licenses and but them. Either from a CSP or MS! You can start out with a trial and use those licenses in the beginning Create the users and Apply a license This is kinda self explanatory when you are in the admin portal It’s hard to help you without knowing exactly what you need!