I have Don Juan Climbing Roses, my problem is: Some of them blooms while others just have green leaves. Some bush may have only one rose on. What do I need to do?

I have this same kind of climbing rose and it is a beauty. Roses require a lot more maintenance, fertilizer and protection from fungus and bugs than regular flowers. Cut the spent flower back on an angle with sharp pruners to just above an outward facing group of leaves. (usually 5 leaves) This encourages branching and new buds. It should be done as soon as you notice the flower is spent to have continuous blooms.