Hello Yash,
In the screen CR01 (Menu/ Logistics/Production/master data/ work center/ create) see the list of Categories appearing. and study in SPRO (Production/Basic Data/Work Center/General Data/define work center category) the commonality of these Categories by going into Application.
You would find one thing common here: i.e.,P - Routings for Production
So, when you give this value in Application to your Category, then it will be appearing there in the list of CR01.
Similarly the entry I (Maintenance Tasklists) in Application would make the Category appear in Tcode IR01. (Plant Maintenance > Environment > Work Centers > IR01 - Create ).
Good luck
KJogeswaraRao