You can easily forward a parked domain to an existing web site. In doing so, when visitors go to the domain being forwarded, their web browser automatically forwards them to the URL you specify.
For example, perhaps you own onecooldomain.com and want people who visit to be redirected to coolexample.com
In order to accomplish this, you need to contact your registrar (the organization where you purchased your domain) as each registrar treats a domain forward differently. Some registrars have a control panel with an option "Domain Forwarding." Others may require your to adjust/add an "A Name" record, in which you will require the destination IP.