Flowers are widely used in gardens, and they're often split into three general categories; perennials, annuals and biennials.
Most flowers fit into one of these categories, where it can give you a good idea of how a plant will behave, when it will flower and how many years it will last. Some flowers don't fit these categories and might for example behave like an annual or perennial depending on where you plant them, but many do.
Perennial plants
Perennials are plants that flower over many years. They can take a while to flower initially, where some do in their first year but many only consistently flower from their second year onwards. Once they're settled and they start flowering they can last for many years, where they get slightly bigger each year if they have space to grow and good conditions.
Some terms often used alongside perennials are herbaceous and evergreen. A herbaceous perennial doesn't have a stem/leaves above the ground in the winter, where it would grow during the warm seasons and die back in the winter. The root growth remains, so when it grows back the next year the plant can grow slightly larger. An evergreen perennial keeps both its roots and stem/leaves through the winter.
Annual plants
Annuals are plants that last one year and flower during this first year, so they can often flower quicker than a perennial/biennial planted at the same time. Many annuals produce seeds, where you can often easily gather these and re-plant them to grow the plant again the next year.
Biennial plants
Biennials are in-between perennials and annuals, where they last for 2 years. They typically grow during the first year and only flower in the second year. Many biennials produce seeds and drop them on the ground to then grow again the next year, so like perennials/annuals you can keep them for many years if you want to.