Richa - Eclipse Juno (4.2) or Eclipse Kepler (4.3) —the 'Eclipse IDE for Java Developers' distribution is strongly recommended by salesforce.com for developments. To know more details abou the Force.com IDE exclipse plugin, check this link https://developer.salesforce.com/page/Force.com_IDE_Installation
Eclipse Luna is will be ok for writing apex classess,triggers and VF pages but You need to install the Force.com IDE into your existing Eclipse distribution. Please refere below link for how to configure Force.com IDE to eclipse. https://developer.salesforce.com/page/Force.com_IDE_Installation
Please refere below link for how to configure Force.com IDE to eclipse.
https://developer.salesforce.com/page/Force.com_IDE_Installation
Regards,
Naveen
www.autorabit.com