help with dekstop connect

I can use it perfect if I am at home and the computer is not put to sleep. (27" iMac)

1.) How do I use this app away from home?
2.) When I try to use it even at home if the computer is put to sleep it will not work. For some reason it wont wake up the computer. I know it can be done because my friend has the same computer and when his is sleeping he turns on the app and the computer screen turns on.

Any help appreciated

 

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