I use ordinary paintbrushes, usually with a good point and a springy feel to them. It's also handy to have a brush with a water reservoir - when you are working on a large section of a painting, it saves constantly dipping your brush in the water pot and losing your flow - literally!
The blocks can be used like crayons for larger areas but my preferred method is to use them like watercolours.
It helps to have a small piece of watercolour paper to test your colours on first and also to use a bit like a palette.
Here I have used the blocks as watercolours to lay down a first layer of colour for the red flowers, making the pigment darker where needed.
And that's as far as I have got with this little painting. The rest of it will be more of the same, building up colour with pencil and washes until I reach the depth I want.
Of course, this is just my style of painting - you could work in big bold strokes with vibrant combinations of colour, it's entirely up to preference. The colours are worth persevering with, the results are lovely.
It is also possible to paint like this on fabric - I have done a couple of t-shirts and several silk ties. But that's a tutorial for another day!