When it comes to flower arranging, you need two things to make the arrangement look right: a water supply and a sturdy base. Smithers makes a product that combines the two into a single piece of material, and is a staple for professional florists all over the world. This product is Oasis Floral Foam, which is easy to find and use.
Decide on the ultimate design of your floral arrangement. Look at pictures in magazines or on the internet, such as a Google Image Search for floral arrangements (see Resources) for inspiration.
Soak the block of foam in the bucket of water. When Oasis foam arrives, it is dry, light and a pale green colour. When it's soaked through, the foam takes on a darker green colour and is a bit heavier.
Cut the the foam with the floral knife to fit the dish you intend to use. Shape it carefully so that it fills the base completely, using the dish itself as a guide. Place the foam in the dish.
Cut the flowers to the length needed for your arrangement. Leave an inch or so to poke into the foam to hold them steady. Make sure the ends of the flowers are cut at an angle, as this allows them to take in more water and stay fresher longer.
Use a cut-off flower stem to poke shallow impressions in the foam to mark the points where the flowers will go for your arrangement.
Push the flowers into the Oasis foam at the marks you made earlier. Start at the centre of the arrangement and work your way outward. Be sure to push them in as far as you can, but angle them correctly before you insert, as the foam does not bounce back afterward---you only want to insert it once.
Place the arrangement on a table, visible and beautiful. Water it every few days, when the foam starts to feel dry.
When the flowers are dead, throw away the foam and the flowers and start a fresh arrangement.
In addition to basic Western-style arrangements, Oasis foam is often used as a beginner material for Ikebana, the Japanese art of flower arranging. Most flower arrangements try to cover the base and foam, while the Japanese style is more minimalist, allowing the base to become part of the arrangement itself. Try different shapes for the foam, such as leaving a rounded inch-tall section above the dish's height to plant things in. You can use toothpicks to attach different shapes to existing pieces of foam.
Floral knifes are sharp, so use with caution.