Putting all together

This is a working source file assembled from the previous fragments. Don't forget to put freemarker.jar into the CLASSPATH.

import freemarker.template.*;
import java.util.*;
import java.io.*;

public class Test {

    public static void main(String[] args) throws Exception {

        /* ------------------------------------------------------------------------ */
        /* You should do this ONLY ONCE in the whole application life-cycle:        */

        /* Create and adjust the configuration singleton */
        Configuration cfg = new Configuration(Configuration.VERSION_2_3_25);
        cfg.setDirectoryForTemplateLoading(new File("/where/you/store/templates"));
        cfg.setDefaultEncoding("UTF-8");
        cfg.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);
        cfg.setLogTemplateExceptions(false);

        /* ------------------------------------------------------------------------ */
        /* You usually do these for MULTIPLE TIMES in the application life-cycle:   */

        /* Create a data-model */
        Map root = new HashMap();
        root.put("user", "Big Joe");
        Product latest = new Product();
        latest.setUrl("products/greenmouse.html");
        latest.setName("green mouse");
        root.put("latestProduct", latest);

        /* Get the template (uses cache internally) */
        Template temp = cfg.getTemplate("test.ftlh");

        /* Merge data-model with template */
        Writer out = new OutputStreamWriter(System.out);
        temp.process(root, out);
        // Note: Depending on what `out` is, you may need to call `out.close()`.
        // This is usually the case for file output, but not for servlet output.
    }
}
Note:

I have suppressed the exceptions for the sake of simplicity. Don't do it in real products.

For the sake completeness, here's the the Product class used in the data model:

/**
 * Product bean; note that it must be a public class!
 */
public class Product {

    private String url;
    private String name;

    // As per the JavaBeans spec., this defines the "url" bean property
    // It must be public!
    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    // As per the JavaBean spec., this defines the "name" bean property
    // It must be public!
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

and the template:

<html>
<head>
  <title>Welcome!</title>
</head>
<body>
  <h1>Welcome ${user}!</h1>
  <p>Our latest product:
  <a href="${latestProduct.url}">${latestProduct.name}</a>!
</body>
</html>