You can apply either offline or online.

For online admission visit http://ignou.ac.in , then go to register online option , you will get online admission section there. Register your self  , after that you can apply online by uploading relevant documents and by paying prescribed fee online for the programme you applied to(polscience and economics).For offline admission visit your near by regional center , the details of which you can get from ignou.ac.in . Buy prospectus  . Fill the form and submit it with relevant documents and demand draft for admission fee.

Hope this will help.