There are five shades in all, each with a helpful notation on the packaging as to what it should be used for. Green is the reducer and neutralises redness in the skin, purple is the revitaliser and counteracts areas of yellowing or general sallowness to remove dullness, yellow is the brightener and lifts the darker undereye area, pink is the balancer and corrects dullness and dark pigmentation in lighter skintones while beige is the highlighter which illuminates the face.
I've found the best way to apply these is directly onto the skin from the bullet before foundation and, working quickly with fingers, blend them in. You obviously just use the ones you need (and, honestly, at almost 11 quid a pop, I doubt many will buy all five) and just work them into the skin until the imperfections have been neutralised and the CC has blended seamlessly. The formula is lovely and creamy with a matte finish so, you won't be left looking like a disco ball but, it does set quickly and wears well throughout the day.
I think you can forgo the beige highlighter shade. It is a bit pointless and very sheer and kind of brings down an otherwise well-rounded collection of colour correcting products. My favourites are the yellow undereye corrector as well as the green redness corrector which I have found to be particularly brilliant for around the nose where women typically suffer with hormonal redness. I have swatched each below but, apologies for how grey my hand looks - I had to do some serious white balance jiggery pokey to get the colours to show up as they are so subtle!