Hi Ayan ,
You can follow these steps:
1. Open the package in SE80
2. Right Click on package & Create Enterprise service.
3. Select the radio button 'Service Consumer' & continue
4. Select the radio button External WSDL where you will specify the url of the external web service i.e. WSDL url given by third party.
5.Save in package & it will create a class along with the ddic structure.
6. Now Activate the code.
7. go to tcode 'SOAMANAGER' & specify the logical port.
8. in SE37 create new program for consuming the external webservice.
Note : Steps may vary according to your version.
Thanks & Regards -
Vishal