what if i cannot find the start using unity button?

I REALLY want to start using unity but i couldn’t find the start using unity button ANYWHERE!!!how can i find it?

When the first time you launch U3D, the Blue Button is there, after the 2nd launch doesnt show the Blue Button because the software is already registered in your computer so you dont need to activate again. But if U3D doesnt start up for the 2nd time - consult Unity, or ask help in the UnityForums