Are you trying to send a single email to email addresses found across multiple records?
Are all the records linked to the same record?
Or are you asking about how to send an email in general?
If you want to send a single email to multiple addresses across multiple records, you will need to have a way to identify which records contain the email addresses you want. If all the records with email addresses are linked to a main record, you can use a rollup field to create a comma separated list of email addresses. However, the records are not all linked to a common record, you have to get creative. You might be able to gather the email addresses using a “Find records” action in an automation, but the resulting list might not be comma separated, and you may need a helper scripting action to insert those commas. Or you can go a pure scripting route, but that will probably require a custom script.