Not sure if my method is the smartest way, but I don’t have many customers yet. You can try: ‘Customers’ → ‘Segments’, then choose “Create Segment” located on the top right corner. This will lead to a page with your customer list, tick those you want to add to your new segment. Click the action three dots (…) then “Add tags”. On the popup, put whatever name you want to call your segment in the input field, then choose “Add”. After that it should show your “Newly Added” segment, click “Save”. There you should have a new customer segment.
To send an email manually to a particular segment, you can do it through ‘Segments’ under ‘Customers’ and choose “Use segment” or go to your Email app and choose any segment under recipients (“To:”).
You can ‘Save as template’ any ‘Automations’ you’ve created, open an automation you want to save as a template, then on the top right corner next to ‘Edit’ there’s a “Save as template” button, click it. This will then show up as your option/template to use when sending email.
Hope this helps!