need urget help ....confuse in st

dear sir . we are new ...we are sole proprietor we register under management consultant ....we received bill against st from vendor .....also we taken service from other vendor and pay their bill with st

so question is if I received my bill with 9.51 lakh st and if I take services from other vender and pay st rs 3 lakh to them so time of at st pay i need to pay rs 6.51 st is it correct

if yes which document we need to keep for this