I have data in two Columns:

A1 - A10 (Room No) (101, 102, 103, 104)
B1 - B10 (Booking Source) (Online, Walkin, FIT)

What I require is to track how many times Room No 101 is
booked which r marked as Online.

Hopefully, this helps get started:
=SUMPRODUCT(((A1:A10)=101)*((B1:B10)="Online"))