What exactly is the email feature for?

I see in the system from the Ranker something about email...

What do I need email for exactly?  and can I do things without it?

Some websites require an email to be used when registering an account. SER uses the emails when registering accounts and then logs in to verify the account, grab login data, etc.

Some platforms require emails and some don't when registering so it depends on which platforms you're wanting to use if it's going to effect your success rate.

I'll say most of the good platforms require a working email. There are many email sellers here on the forum that charge around $10 for 1,000 emails or close to that.

$10 per 1,000 emails sent?  Or 1,000 email accounts?

How many emails can I send per account? 

It's usually around $10 per 1,000 email accounts but it can be +- a few dollars. 

There are a few email account sellers here on the forum.

Banditim sellers some here:

https://forum.gsa-online.de/discussion/13667/yahoo-accounts-14-1k-pop3-enabled-spam-filter-disabled-instant-delivery and here https://forum.gsa-online.de/discussion/14512/nokiamail-email-accounts-10-1k-spam-filter-disabled-instant-delivery

Also some here: http://buybulkaccount.com/

And pretty cheap here: https://www.fiverr.com/satyr85/provide-625-yahoo-email-accounts

I'm not sure what you mean how many emails can you send per account. You won't be sending emails, the emails will be receiving account information when registering on websites. You just import the emails into the software and click the "test" button to make sure they're working, then the software will handle the other stuff.

I usually import around 3-5 emails per project unless I think I might need more.

Thanks... useful information