Before we start, there are three ways to do this.
You can set up mailboxes for each email address, this is good if you have, for example, multiple employees or family members. Each person then become responsibles for checking their own email. If it is just you and you create multiple mailboxes (rather than forwarders) it will mean you have to check email account separately.
For an individual who wants, for example, hello@, sales@, support@ but wants them all in one mailbox, choose a primary address e.g. hello@, as your mailbox and then set up forwards to that for the other addresses.
You can also forward emails for your new domain to an existing webmail account, but it is not the best solution.
If you like gmail, the best and easiest email solution is to fetch emails for your new domain to an existing webmail account e.g. gmail. You then get all your email in one place.
Perhaps you are looking for how to set up gmail to send emails from You@YourDomain