SPF & DKIM, how & when to use?

Hi,
am seeing the SPF & DKIM tab and just need a little more clarifying..
When should i use this, and how?

So, say, my website is domainname.com
But in the Advanced tab i chose [email protected] to be my sending email address.
Note that [email protected] is an email address which is using the GSuite (Google Apps) service.

So, to which domain should i add these SPF & DKIM records?
To the domain where my WP website is hosted? (domainname.com)
Or to the domain i chose to send emails with? (otherdomain.com)

Your guidance would be much appreciated.