Hi Kaan.
I hope you are trying to develop Fiori like custom application.
To build SAPUI5 applications you would need UI5 plug-ins which can be installed in your Eclipse from either SAP Development Tools for Eclipse - Luna Software Repository for Luna or SAP Development Tools for Eclipse - Kepler Software Repository for Kepler.
Look at this link - SAP Fiori - Developing Custom Apps for move info on developing custom apps.
Please follow the space - UI Development Toolkit for HTML5 Developer Center for discussion,blogs and documents.
Hope this helps.
