First thing is to make sure your indicator or EA uses the right programming language. cTrader user C# unlike MetaTrader’s MQL4 and MQL5.
Then the easiest way is to install an algo file. Simply double-click the file and cTrader will open the file and ask to install the EA.
If this does not work, this would be because your operating system does not recognise algo files, you will need to open your documents folder using windows explorer and navigate to the Sources folder, here you will see two other folders, all you need to do now is open the relevant folder and copy/paste the algo file into this folder, this will automatically install or replace an existing file.
* Tip: if you have many indicators to install, the fastest method is second method.