Hi Sachin,
Please provide us the below information for better assistance.
1. Is your Gmail account converted to the Microsoft account?
2. What happens when you try to sign in to the Windows Store?
3. Do you get any error message/code? if yes, then provide us the complete error message/code.
If the you have not converted your Gmail account to the Microsoft account, then you cannot sign in to the Windows Store.
Please refer the below link about benefits of Microsoft account with Windows.
https://www.microsoft.com/en-in/account/default.aspx
Let us know if this helps. Keep us informed for further assistance.