Hello Freed Gerdes
Welcome to the forum.
I sincerely hope that you do not have to "create a fictitious entity that is" your true name. Presumably you already have a true name, which your parents should have created for you around the time of your nativity. Keep it and cherish it. It's a sound which may identify you in the minds of other people.
More than likely you also already have a fictitious entity created around your true name, which involves your family's name, and perhaps some suffix, which is spelled in all caps and tends to be used as "state inventory" like you said. It's a numbered account which you would use to obtain "privileges", which are far less useful to you than they are to government employees who are glad that they don't have to get real jobs in the productive sector.
The less you can use that fictitious entity, the more you will probably enjoy yourself.
As far as buying a car with lawful money is concerned, David Merrill has some examples somewhere on the forum, but I can't remember where he posted them.
Perhaps he can provide the link if he sees this post.
Where to stamp a FRN is a nice thread about lawful money, which you may enjoy participating in.