1) Did I read right that it will work at all airports in FSX?
Of course, that's exactly what the site clearly says what GSX does...and on top of that, is totally free on all FSDT and Flightbeam sceneries, so if you have any of them, GSX will work there even without a registration, just like the full version.
And either uses stairs or jetways ? Depending if the jetways are able to move ??
It uses front stairs if the parking doesn't have a jetway. If you have a 3rd party scenery that doesn't have moving jetways or have non-standard jetways, GSX cannot detected automatically, so there's an option in the GSX scenery customization page, where you can say, parking by parking, which of them have a fake/static jetway, so GSX won't try to display front stairs and a passenger Bus there.
2) I tried to use it at EDDM with Aerosoft scenery but couldn't get the jetway to move?
You should probably suggest to Aerosoft they should consider releasing airports with working jetways, a feature that even default airports have. That won't *prevent* AES to work there in any way, but it will surely increase the perceived quality of their product...one would imagine that a payware scenery would AT LEAST match the default scenery features!
And kept getting this message saying waiting for exit 2 ??
Since you don't say which airplane you were using, I can't say if you simply tried to load baggages with the cargo doors closed (why would you??), or you tried to use an unsupported airplane and haven't made a custom configuration for it, so the cargo door was indicated with its generic default name and control, but the 3rd party add-on airplane you used had a different mapping for that door.
3) Do I need to select the com freq for the jetways to move if I've got add on scenery ?
If the 3rd party add-on scenery you use requires the use com frequencies to move its jetways (which is a very old method used many years ago), having GSX installed or not won't change this.
If the 3rd party add-on scenery you use have proper native FSX animated jetways, like all the more recent products from the best scenery developers out there ( all FSDT, Flightbeam and many from UK2000 are all made that way ), then you use the standard CTRL+J command, and having GSX installed or not, won't change this.
If the 3rd party add-on scenery you use doesn't have animated jetway at all, having GSX installed or not won't change this either.
4) I imagine you need to configure the doors and pushback truck similar to AES or am I getting confused?
If you want to add an unsupported 3rd party airplane to GSX, then yes, there's a configuration utility included, fully explained in the GSX manual, of course.