The easiest method to install FreeRDP on the Ubuntu is from the repositories, sudo apt install freerdp-x11
(or freerdp2-x11, depending on the version you want) will do it for you.
Note that FreeRDP is a client to the RDP protocol; it works as a desktop application. So, you cannot use it from within the browser, at least not directly.
In principle, you either start xfreerdp from the terminal with the appropriate connection parameters, or if you want the GUI tool, I can recommend Remmina.
If the access to the remote desktop from the browser is mandatory, you may additionally install the Apache Guacamole server, which can (roughly speaking) convert RDP protocol to something that browsers can understand.