In general, there is no minimum sized order to invest or sell on pearler. You will have to buy or sell a minimum of one unit, and the cost of one unit varies depending on the particular stock you are interested in.
The one exception to this rule is for free ETFs. All free ETFs have a minimum invest/buy size of $500 per transaction of a given stock. There is no minimum sell size for a free ETF stock. To enjoy the benefit of the free ETFs, you will need to hold them for at least a year. However, if you sell some or all free ETF stocks within a year, a 2xbrokearge fee will incur when you sell them. Read more about free ETFs.