Download the free App (Microsoft Remote Desktop) from the Apple App Store:
https://itunes.apple.com/us/app/microsoft-remote-desktop/id715768417?mt=12
Open the App and Press:
New Remote Desktop
When prompted at this screen provide the information TkFast has given you:
Connection Name: Just a unique name so you know what computer you are connecting to, i.e. Work.
PC Name: IP of computer you are connecting to.
Username: Login Username to computer
Password: Computer Password
When login credentials are correct, press "SAVE." You'll be taken back to the mainscreen when you select the connection you just configured and it will connect. Once connected, if you'd like to disconnect press the name of the connection at the top of the screen and press the icon on the far right that looks like two plugs.