E A Mystery

I would like to try some of the EA’s so generously offered in various forums on the net.

#1 How can I distinquish between an indicator and an EA.
They both seem to be *.mq4 files?
#2 Sometimes I see a *.set file. What is this and where do I put it?
#3 Sometimes I see a *.tpl file. What is it and where do I put it.

If some one knows a web site that explains all this…I would appreciate knowing the URL.

Thanks