The most common method to buy stocks is to use a brokerage.
Brokerages come in a few different flavors.
Discount brokerages offer little in the way of personal attention but are much cheaper. These are plans in which individual companies allow shareholders to purchase stock directly from the company for a minimal cost. Drips are a great way to invest money at regular intervals. In order to make your trade you'll have to be specific how the security should be traded. An order that expires at the end of the business day if it has not been filled.