Auto-Size Your Text Boxes
Typically when you create a text frame, the frame size is set to the height and width you initially created it at.
When you paste in text or type text in a text frame that exceeds the size of the frame, you get one of those red + icons on the frame edge to let you know there is more text in the frame that isn’t visible.
To allow your frames to automatically resize or expand according to the size of your text (without you having to manually extend the frame), go to Object > Text Frame Options. In the dialogue box, select Auto-Size at the top then select “Width Only” (or any of the other options there if the orientation suits you), and in the box below, select the left to right icon (meaning the text box will expand out to the right). You can also select the centre icon meaning your box will expand to the left and right equally, or the right to left icon, where your box will stay stationary on the right and expand outwards to the left.
As you can see here, the red + icon is gone and the text box automatically expanded to include the rest of the heading.
This setting is useful if you have multiple headings or blocks of text of different widths/heights over several pages.