All I need, is for someone to explain me how to create such a system, [...]A basic step-by-step post, explaining this would be awesome
That would be nice, wouldn't it?
Unfortunately that post would be miles long for this is a non trivial task you are asking, especially since you want to use MS Access when MySQL is more used and thus better supported by this community.
Your best bet is asking questions and us answering them. I don't think anyone is going to do a step-by-step for you... and if they do, god bless them!!!
The problem is, that I want the entities unique ID to be the same as the user's ID in the database, but I'm stuck on this and don't know a way to do this...
Simply pull the entities unique ID from either it's handle or client number and use that in the database.
Is there a way I can create the invisible entity and parse all the data (strings, variables, etc.) from the client to him
No. An entity only received skills to be used in it's actions. An entity does not recieve strings and thus can't parse them. Your idea however is sound if you take away the entity. With the new Client Number, you no longer need to create a separate, invisible entity to reference your client; the client receives a unique identifier the second it connects to the server. Thus all you have to do is send_string_to(client_number, message_str); and then have the parsing function in the STRING HANDLER, not the entity.
