To add an expert advisor (EA), first you need to open the MT4 Client Terminal, click on `File` on the top navigation menu, and select the Open Data Folder in the drop-down menu. In the Open Data Folder click on MQL4 and Experts. The Experts folder is where you can add the expert advisors (EAs). Paste the .mq4 or .ex4 EA file into the Experts folder. Once you are ready with this, restart the MT4 platform by closing it and then reopening it.