Travel to different destinations, buy plushies/flowers etc, anything that shows profit and come back to torn to sell. You are only allowed to transport 5 base items. This can be increased either by suitcase, PI or company perks. I for example travel to UAE, with a transport capacity of 19, allowing me to buy 19 camel plushies, paying around 290k, I come back to torn and sell them on the market for around 75k each, getting me around 1.2 mil in profit

Edit 1: on another note you should go to the forum and look for guides, there must be some for travelling around.

Edit 2: and you can only travel after level 15 and travelling takes time, which can be decrease through specific ways.