I just entered "quickbooks c#" into Bing and got numerous hits. The obvious web search should ALWAYS be your first option. If you get no results, then you can ask a question on sites like this. If you do get results, then you can do the appropriate reading, put the information you find into practice and ask a more specific question on sites like this when you run into a specific issue. Sites like this are great for stuff that you can't work out for yourself but should not be used in place of a search engine.