You can configure Sitecore to respond to requests with different home nodes based on the url.

To do so, you need to perform the following steps:

1. Configure DNS appropriately.
2. Add a binding in IIS for each hostname.
3. Copy or rename the config file `App_Config/Include/SiteDefinition.config.example` to `App_Config/Include/SiteDefinition.config`
4. Modify the config file from step 3 with a new `<Site>` node for each site.

For example:

    <!-- this entry will respond to http://site1.hostname.com/mysite with the /Sitecore/sites/mysite/home node -->
        <site name="SiteName" patch:before="site[@name='website']"
    	    hostName="Site1.hostname.com"
                virtualFolder="/mysite"
                physicalFolder="/"
                rootPath="/sitecore/sites/mysite"
                startItem="/home"
                database="web"
                domain="extranet"
                allowDebug="true"
                cacheHtml="true"
                htmlCacheSize="50MB"
                enablePreview="true"
                enableWebEdit="true"
                enableDebugger="true"
                disableClientData="false"/>

For more information see: https://sdn.sitecore.net/Articles/Administration/Configuring%20Multiple%20Sites/Configuring%20Sites%20in%20web,-d-,config%20File.aspx