Ideas for colourful flower bed

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Some advice- I'm new to gardening... I have a layered front garden with path in the middle, I'd like to fill up the beds much more and I love a very colourful flower display...
See photos of my garden and then the ideas I like.
I love the flowers to be all the same in a row to create a dramatic look like they have in the parks..smaller flowering plants at front, larger more to middle... (I have the palms and phormium plants in middle of the beds already as I like those tropical plants and plenty of space for them in the middle) 
Do I just go out to somewhere like Tesco and buy loads of bedding plants? And will I need to replant every year? 
Which flowering plants would stay from year to year? 
Do I create a heap of soil so its higher in the middle?

JennyJ

Your examples are traditional bedding displays which are normally done with annuals, planted densely and replaced twice a year - tender things for summer and then replace in autumn with things like forget-me-not and wallflowers interplanted with tulips or daffodils for a spring display. And yes, traditionally the soil would be mounded up a bit in the middle for island beds (that can be viewed from all around). It's a style that's not commonly seen in private gardens these days (not around here anyway). It reminds me of my grandad's garden - every summer he had a bed planted with red annual salvias or pelargoniums with blue lobelia and white alyssum around the edge.

The second pic, is I think, bedding begonias (the fibrous-rooted kind) - white round the outside and pink in the middle. Although the white could be impatiens (busy lizzies). In the first pic the red flowers are probably also bedding begonias, then there's a row of (I think) coleus, but I don't know what the dark-leaved plant is.

You might be able to get a similar effect with perennials but generally speaking they don't flower for as long.