First of all You need to setup DNS records as mentioned in the previous answer.
If You are new to DO, and it's seems to complicated for You,
You have ability to point Your domain name to the DO IP address. ie. create A / CNAME records matching Your domain name / IP address in the GoDaddy DNS pannel.
Next thing You have to do is to configure apache daemon (I assume that You are talking about web applications), so the server can understand when it receives requests from Your doamin name, and it must know where to point that request to. (path where you web application is stored) /etc/hhtpd/conf/httpd.conf