The algorithm can have an infinity on functions and one can be to send trades but in this case you also need one on your terminal to receive the trades.
In alternative the signal service doesn't require EA's to send and receive trades, just subscription and terminals always connected to internet.
I guess beginners all go for signals...
EAs maybe are for people more into coding, right?
Shloss take a look to this links,they should be usefull to understand strategy tester:
the anwer to your qustion about spread is inside this post: