It's hard to imagine life without T-shirts, because even if you spend ages thinking about what to wear: in the end, it can always be a T-shirt. T-shirts come in prints, plain colours, tight, loose or oversized cuts.
Either round or V-necks are particularly popular. For a particularly well-rounded outfit, it is advisable to always pick up a colour from the T-shirt in the bottom. For a casual look with a highlight, you can of course wear a T-shirt in a bright colour and keep the rest neutral to set off the colour perfectly.