You need to follow all the local regulations from the aviation authority in the country in question. I can tell you what typical where I fly but this may vary. Most of the information for Dresden is listed here but in general:
You will likely be met by a marshaler who will show you where to park after you land and get taxi directions to your ramp of choice.
Typically transient GA planes are left locked, with the parking break off so that ground crews can move them about the ramp without you. Ive never left the keys to my plane with a ground crew and wouldn't even if asked. They dont need to get in my plane to move it. They will likely instruct you on what to do when you power down. The typical call out in the states is "parking break off?" before the marshaler drives away in his golf cart...
If you cross a border and need to clear customs you need to make sure that the airport in question has customs and then you will need to deal with any arrangements you may need to (including paperwork) before hand to make sure you can actually get cleared.
Most airports where I fly have some kind of an office/fixed base operations/management facility where you can physically exit the field (and it appears Dresden has a nice lounge). This is typically where you also pay for fuel and overnight parking. You will return through this facility as well. Again most major airports are open 24/7 (even GA facilities) but you should confirm this with them in advance if you intend on coming and going at odd hours.
You will not need to go through "security" in the typical airport sense to get back to your aircraft since you are using the private terminal. However as noted above you may need to organize some customs related things.
Also of note, if you are flying into a busy city airport they will expect you to be on top of your stuff. You may need to read back long taxi instructions, wait for a while on a taxi way for other flights to leave etc.
Here is a fascinating series of videos on flying into a country that has almost no GA support