A. I want to complete my 12th Standard class from outside by giving the exam of Book Keeping & Accountancy subject.
It is 12 years since you have taken your 12th standard exams. Good to hear that you want to graduate. Now you need to appear as a private candidate.
The other option is the National Institute of Open Schooling (NIOS), a Government of India program for people in your situation to encourage them to study and also get a vocation based training too.
Please read this carefully (http://onlinecd.nios.ac.in/niosreg_region/streamIVinfo.htm). This is on demand senior secondary (12th) exams where in candidates who have appeared the regular exams from any recongised board but could not clear the exams. This would be applicable to you, your subject Accountancy code is 320.
Once you enroll, you can download or request the study material related to your subject (http://nios.ac.in/media/documents/requisition.pdf). The cost for three volumes of study material is Rs 350.00
Once you pass, the certificate which you are given is recognised for other higher education center.
B.After I give 12th class Book Keeping subject can I do B.Com exam from anywhere?
Yes certainly, you can do your B.Com. If you enroll in IGNOU, you can complete you B.Com in 3- 6 years with the fees being Rs 6,00.00. There is no age limit for this in IGNOU. After this you can do your masters too.
If you want to choose any other graduate in arts, literature etc in IGNOU, that is also possible with the NIOS XII clearance certificate. By this means you can continue working and also complete your studies without needing to lose time off employment.