Hi
Yes you can study bcom as a degree even if you have arts in class 12th.
Some universities offer an Honours program to those who have studied maths in 12th while others provide students with an opportunity to enrol in a generic bcom degree.
Here are some of the subjects taught in this course -

Banking and Finance

Foreign Trade

Banking and Insurance

Logistics and Operations

Computer Application/Science

Accounting and Finance

International Business

Taxation

Human Resource

Law