Esther, You are about to embark on an interesting adventure as a professional florist. The flower arranging courses will help get you started, but I would also encourage you to work for a short term for an existing florist (to see how some things can be done) and also to develop a business plan. A great book to get you started is the E-Myth by Gerber.
Fresh flowers, whether shipped dry or in a floral preservative solution, need to have the stem re-cut under water. This is done by holding the bottom two inches of the stem under water and removing the bottom one inch with a sharp knife or scissors. The cut doesn’t have to be angled, but it does need to be made under water to restart the flow of water up the stem.
Water tubes are used to ship some flowers, especially roses, that don’t travel or ship well dry (without floral preservative). The process of rehydrating flowers is what happens when you recut the stem under water for a flower shipped dry and then put into a solution of water and preservative to get the water flowing up the stems to maintain the flowers’ longevity.