If You want to claim input tax credit on purchases & documents needed in BUSY Follow below steps:
1.When you enter Purchase Voucher In BUSY Option Shows
2.ITC Eligibility in that you Can Select on these options
3.Input Goods/Services, Input services, Capital Goods/Services, Section 17(5)-Ineligible ITC, Section 16(4)-Ineligible ITC, ITC Restricted Due To Pos Rules.
4.In BUSY ITC Depend on Chooseing on that options.
5.For Documents You Can Download GSTR-3B.
6.In GSTR-3B you can find your ITC Tagging.