Here is the Amateur Flower Arranging How-To: Oasis.
And that concludes the tutorial, thank you for your rapt attention.
Haha just kidding, you know I have way more words than that.
I have never had any classes in flower arranging or floral artistry and when you dig deeper you will find that there is MUCH more to beautiful and long lasting arrangements than just Floral Foam that can hold water - aka "Oasis." For my purposes I'm going to ignore all that and just share how easy it can be to make a pretty arrangement with no expertise whatsoever and some very affordable materials...
Materials: An opaque container (Oasis isn't pretty)
Oasis Floral Foam (foam that holds water)
Scissors or garden clippers
Possibly a plastic bag (depending on your container)
You can go further and add ribbons, tags, glitter, jewelry, chocolates, diamond rings, promises of undying love and fidelity, backup singers, film crew, photographer etc. but it's certainly not required. I do like to add a ribbon pretty much always (I have a ribbon collection/problem) and I usually add a tag or a note if the arrangement is a gift.
1) Cut your Oasis to fit inside your container
2) Soak the Oasis in water until it is completely saturated.
3) If you have a container that might rust or leak (tin can, basket, terra cotta pottery etc) you will need to wrap a plastic bag around the wet Oasis to prevent a mess.
4) cut an inch or two off your flowers and get them into a water pitcher that has some flower food in it (I also like to soak the Oasis in water that has floral food in it).
5) Select a flower and peel off any leaves or buds that would get shoved into the floral foam.
6) Measuring your flower against the height of your container snip off excess stem and gently push the stem into the floral foam wherever you think you would like it to be.
Note: if the stem bends the bloom is going to look dead the next day in most cases so you want to be gentle and if the flower is resisting you probably need to trim a little more length off the stem instead of just pushing harder.
7) Repeat step 6 again and again and again until you have a lovely full arrangement and you can no longer see the floral foam.
8) Look over the finished arrangement and make any adjustments you feel are necessary (moving flowers from one place to another, lifting or raising blooms higher or lower in the arrangement).
9) Add additional water to your arrangement to keep the floral foam wet as the days go by - if your container is not watertight and/or rust proof be careful to make sure the water is getting inside the bag you used as a liner.
I like to use wired ribbon because it is more obedient but that is not required. I just form a center loop sized appropriately for the size of my arrangement and pinch that with my fingers while I form more loops behind that until I have about 4-6 side loops. Then I run a wire down the middle of the center loop and around the back and tie it all off like a twist stem. I use the wire on the back of the bow to attach to the handle of the arrangement or simply poke the wire into the floral foam like another flower. Then my favorite is cutting the ends of the ribbon into a swallow tail (fold the ribbon end in half and cut on the diagonal). Done and Done.