I found out that you need to get the words of power (before) I kill dragons. I want to know is their a limited number of dragons in the game or do they keep spawning until you complete the main qwest?

Dragons that you kill in certain areas will respawn given time. I'm not sure how long you have to wait, but I know for certain they respawn.

hey thanks.

I also wanted to say is that I found out that you store the dragon soals on you. When you open up the shouts menu there are listed on the lower rite. So I never really lost them. Also found out that unlike the first shout that gets unlocked attomaticly when you kill your first dragon (main quest). You have to select the word and then check in the lower rite and see unlock word. If you a stored soal, you can unlock the word. Have fun