You can buy 1 share or 1,000. Most brokers will have it automatically set to buy 100 when you are placing an order, but you can change it to whatever you want.
Just remember about the commissions. If you’re paying $7 per transaction then obviously you don’t want to buy 1 share, because it would have to go up a lot to break even. You’ll want to buy enough so that the brokerage fees are not going to kill you, but other than that it is however much or little you want to buy.
