When thinking about circuit design, there are two really, really high-level categories to consider: through-hole and SMD. Through-hole is the traditional component style that has conductive leads that are fed through holes (roll credits) drilled in a circuit board. The leads are then soldered to conductive pads that surround the hole, and the remainder is trimmed off. SMD, which stands for surface-mounted device, is a component that is installed via SMT (surface mounting technology). These are soldered directly to pads on the circuit board, without leads or holes. SMD components are generally much smaller, and occasionally cheaper, but more difficult to handle in an amateur, DIY set-up. Some hobbyists fully embrace it, but my eyes aren’t keen enough for the tiny sizes and my hands aren’t steady enough for the fine soldering work.
Since I don’t work with SMD as a general rule, my descriptions of electronic components are related to through-hole, unless otherwise noted.