If you are investing with a fund house for the first time then a new folio will be created by the fund house. While placing subsequent orders with the fund house, you can select the existing folio on the cart page. 

While selecting a folio on cart you can also mark it as the default folio for future purchase orders in the same fund house.

There is no restriction on the number of folios that you can have with a particular fund house, we recommend that you have a minimal number of folios for ease of monitoring your investments.