Hi akshat,
Cash Memo/Sales Receipt is meant to capture cash sales, i.e. sales transactions in which funds are realized when the service is rendered or the product exchanges hands.
Invoice is meant to record credit sales, i.e. sales transactions where there is a gap between the rendering of services/sale of the product and the realization of funds.
Here's article with information on creating these transactions in QuickBooks.
Should I use an Invoice or a Sales Receipt?
https://community.intuit.com/articles/1761165
