To access the Mac from a Windows machine, you will need to install a VNC client on the Windows machine, or locate RDP server software for the Mac (not sure if it exists). I use VNC myself since it is ubiquitous, easy to set up, cross-platform and essentially open source. However, be aware that it is not a very secure protocol since it lacks sufficient encryption or even a username parameter. All the same, it is still widely used in secure environments. The VNC protocol can also be hardened by tunneling it through SSH, but that is a topic for another day.
To enable VNC on the Mac, navigate to SystemPreferences>Sharing>RemoteManagement. Make sure this feature is enabled (as you say you have already done). Then click on the "Computer Settings..." button. In the new window, place a check to enable "VNC viewers may control screen with password:" and then set a password.
Back on the Windows machine, install your prefered VNC client and launch the program (I prefer TightVNC). Enter the IP address of the Mac and the password you previously created in the Mac's settings if needed. If you are not asked to supply the password in the VNC client's connection settings, you will be prompted for it after the connection begins to take place.