There are two ways to point your domain to SiteGround: using SiteGround nameservers or an A record.
Option 1 – SiteGround Nameservers
To find the required nameservers, log in to your SiteGround account. Once there, go to your Client Area → Websites → Site Tools.
You'll find the necessary nameservers in the Site Information section.
Copy the given nameservers, and specify them in your domain's DNS zone.
If your domain is pointed elsewhere by NS records, your DNS zone is also managed from there
Option 2 – SiteGround A record
Alternatively, you can point your domain to SiteGround via A record: you can copy it from the Site Information → Website IP.
Once you have the required IP address, create an A record in your domain’s DNS zone.
After you add a new A record, DNS propagation will start. This process can take up to 24 hours. During this time, it's expected that your website won't work, but give it some time, and it will get online soon.
That’s it! Now you know two ways of pointing your domain to SiteGround.