Money

You will find life in the 21st Century to revolve around a illusionary commodity called money. Money is manufactured by the faction leaders and given liberally to their enforcers in return for them making sure all the slaves pay money they do not have to the faction leaders in the form of "taxes".

"Taxes" are a form of stealing where the taxor threatens the taxee with punishment if the taxee does not pay the taxor some portion of his labour as he goes about trying to get the bear essentials in the world. "Taxes" are paid to faction leaders in the money that the faction leaders create for free. The faction leaders are not in need of their own illusionary commodity, but manage to ensure that the slaves work for in exchange for this freely created commodity so they can avoid punishment for not paying taxes to the taxors.

You will find it impossible to exist in the 21st Century if you don't pay taxes since you cannot work or trade without the faction leaders intervening to get a cut from all means by which a person of the present day earth can sustain their own lives.

If you have just arrived from the 28th Century you are advised to forge a passport to pretend you're from the 21st Century and get yourself a job where you will be taxed by the faction leaders but you will get to keep whats left of your earnings from employment to pay the taxes when you come to spend what you have left over. If you are lucky, you should get enough food and shelter to sustain your own life until you can source spare parts for a domestic compact fusion reactor to power up a food supply chamber inside a physicality cloak which will conceal your presence from the 21st Century people who would never believe that time travel is possible.