To add an EA, open MT4 and then go to ‘file’ and then ‘open data folder’. Choose ‘MQL4’, and then ‘expert advisors’ or ‘indicators’. You can then copy the file you want to add into this location. Close and reopen MT4, and you should see the item in the navigator window.
If you didn’t make the EA or indicator then be sure to test it in with your demo account first.