Good documentation at https://nosqlnocry.wordpress.com/2015/03/05/setup-eclipse-to-start-developing-in-spark-scala/. But in case you still need help:
- Use Eclipse Juno release. L has some problems
 - Install scala plugin from http://scala-ide.org/download/current.html
 - Create maven build, sample pom.xml and you are good to go.
 
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId></groupId>
  <artifactId></artifactId>
  <version></version>
  <packaging>pom</packaging>
<properties>
  <maven.compiler.source>1.6</maven.compiler.source>
  <maven.compiler.target>1.6</maven.compiler.target>
  <encoding>UTF-8</encoding>
  <scala.tools.version>2.10</scala.tools.version>
  <!-- Put the Scala version of the cluster -->
  <scala.version>2.11.0</scala.version>
 </properties>
<pluginRepositories>
<pluginRepository>
    <id>scala-tools.org</id>
    <name>Scala-tools Maven2 Repository</name>
    <url>https://oss.sonatype.org/content/repositories/snapshots/</url>
  </pluginRepository>
</pluginRepositories>
<dependencies>
  <dependency>
    <groupId>org.scala-lang</groupId>
    <artifactId>scala-library</artifactId>
    <version>2.11.0</version>
  </dependency>
  <dependency>
   <groupId>org.apache.spark</groupId>
 <artifactId>spark-core_2.11</artifactId>
 <version>1.4.0</version>
  </dependency>
</dependencies>
 <build>
  <resources>
      <resource>
        <directory>src</directory>
      </resource>
    </resources>
        <plugins>
<plugin>
  <groupId>org.scala-tools</groupId>
      <artifactId>maven-scala-plugin</artifactId>
      <version>2.15.2</version>
      <executions>
        <execution>
          <goals>
            <goal>compile</goal>
            <goal>testCompile</goal>
          </goals>
        </execution>
      </executions>
</plugin>
<plugin>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>2.4.1</version>
    <configuration>
     <descriptorRefs>
      <descriptorRef>jar-with-dependencies</descriptorRef>
     </descriptorRefs>
    </configuration>
    <executions>
     <execution>
      <id>make-assembly</id>
      <phase>package</phase>
      <goals>
       <goal>single</goal>
      </goals>
     </execution>
    </executions>
   </plugin>
</plugins>
</build>
</project>