Online business

my client have its own website and have one domain name and he wants to start online business of selling goods as per order received by him. he wants to know that whether he charged vat on his invoice or not. and also what is proper treatment as per sales tax act. And one another problem is that he purchase goods in loose and dont take any bill from seller and also do not pay any tax on purchased goods and when he sell those goods under his domain name whether he is required to chargd vat. if not what complications he can face as per taxation point and law point of view i am requested you that plzź advise. or give me mobile number so that i can call you and take solution of may problem from you. thanks........