As a beginner, focus on a maximum of one to two stocks during a session. Tracking and finding opportunities is easier with just a few stocks. Recently, it has become increasingly common to be able to trade fractional shares, so you can specify specific, smaller dollar amounts you wish to invest.
That means if Apple shares are trading at $250 and you only want to buy $50 worth, many brokers will now let you purchase one-fifth of a share.