Summer flowering shrubs like so many shrubs create structure and shape in the garden.
Many shrubs are easy to grow and low maintenance, providing colour for not too much hard work. As with all shrubs, they have individual growing requirements, but one general point to check is the eventual size of the shrub. The plant label should give this information as it's important if the shrub is not to swamp other plants in the border. For example right is hydrangea lovely but quite big a spread of 1.5m so it will take up a fair amount of the border. Similar the Buddleja which is great for attracting butterflies and pollinators, but matures to a large shrub.
Below are illustrations and links to information about individual summer flowering shrubs, their preferred growing conditions, eventual size and everything you need to know about growing summer flowering shrubs.