how to use custom css file in sharepoint 2013

I am extremely new to Sharepoint and have started exploring sharepoint 2013.

I have downloaded copy of seattle.master and created my own master page called MyFirstMaster.master.

Then created new empty sharepoint solution in visual studio 2012 added my master page. Then deployed solution. So far so good.

Now i want to have my own css file so searched in master file and found that it is using this

<SharePoint:CssRegistration Name="Themable/oslo.css" runat="server" EnableCssTheming="true" />

So i added one more line below which can use my custom css

<SharePoint:CssRegistration Name="Themable/MyCustom.css" runat="server" EnableCssTheming="true" />

I also included MyCustom.css file in below path same as it was for oslo.css

C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\LAYOUTS\1033\STYLES

Then i deployed solution but still its not using my css file. I dont have sharepoint designer. How can i use my own css file.