If your domain is pointing elsewhere by NS records, your DNS Zone management is moved to the provider you pointed the domain to and should be managed from there
What to use as a Name (Host)?
If you are adding MX records for your domain, insert @ as Name.
If you are adding MX records for your subdomain, insert the subdomain’s name as a Name. For example, for subdomain support.domain.tld you should use support as a host.
What to use as a Mail server (Points to)?
The value on Mail server will be the MX records to which you want to point your domain. To see which records you will need, check this article: Where can I find Hostinger MX records?
What to use as Priority?
Priority for MX records is defined by the mail service you would like to use. Each record will have a priority and typically will be in increasing numbers. For example, if you're using Hostinger free email services, the mx1 record, uses 5 as a priority, and the mx2 record uses 10 as a priority.
What to use as a TTL?
It is recommended to use the default which is set to 14400 seconds (four hours).
How to edit or delete MX records?
If you want to edit an existing record, check this article: How to manage my DNS records on hPanel?
Any DNS Record changes trigger propagation, which can last up to 24 hours to fully propagate.