premiere pro cs6
When you add an effect like a transition or a title to your sequence, it may need to be "rendered" so it displays properly on your computer screen.
Rendering means having the effect processed by the computer so it is permanently added it to your sequence of clips. If you see red or yellow lines above your Timeline, those are areas of your sequence that need to be rendered, usually because you added effects there.
To render all the effects in your entire sequence, in the menu at the top select Sequence...Render Entire Work Area.
The work area is the gray bar with the orange end points that's above all the tracks in your sequence. You can reposition the work area, and hence the portion of your sequence being rendered, by dragging the orange end points left or right.
It will take some time for the rendering to be completed depending on how complex the effects were that you added to your sequence.