DNS can be a bit tricky at times. It looks like your email provider is asking you to add these DNS records to a domain with DNS managed by DigitalOcean?
They're asking you to add a CNAME, two MX records, and a TXT records. The CNAME record will allow you to easily access your webmail by going to mail.test.estate. The two MX records will tell other computers how to route email coming to you, and the TXT record is for sender verification.
To add the CNAME, click "Add Record", choose "CNAME", set "Name" to "mail.test.estate" and "Hostname" to "oxwebmail.registrar-servers.com." then click "Create".
To add the two MX records, follow the steps above, except choose "MX" instead of "CNAME". Your "Priority" will be "10" for both records we're going to create. For the first "Hostname", use "oxmail1.registrar-servers.com.", and use "oxmail2.registrar-servers.com." for the second one.
Last but not least, the TXT. Follow the same steps as before, but choose "TXT". "Name" should be "test.estate" and "Text" should be "v=spf1 include:ox.registrar-servers.com ~all".
I hope this helps! If you need any clarification, please don't hesitate to ask. I've also included example screenshots below.
CNAME Example: http://cl.ly/UMXN
MX Example: http://cl.ly/UMrM
TXT Example: http://cl.ly/UMPL