For U.S. investors, buying and selling stock like iConsumer (RWRDP) on the OTC Market has a pretty clear roadmap. Just sign up at just about any online brokerage (our favorites are TD Ameritrade for beginners and Interactive Brokers for the more experienced).
Some brokerages charge an extra fee, or won't trade low-priced stocks. So, they're not good for trading stock like RWRDP. As of March 30, 2018 we know that Ally has a surcharge, and Robinhood doesn't support them.
For people located outside of the United States, there are fewer choices. As it happens, once again our favorite choices are TD Ameritrade and Interactive Brokers – list of countries.