Have a look at this screenshot:
On the left, the paragraphs are separated by a standard paragraph return. The keystroke is the wide Return key (sometimes labeled Enter on some keyboards) that you see at the right side of the keyboard above Shift. If there is room in the text frame (in InDesign, it's called a frame, rather than a box—that's just FYI) then the amount of text that will fit will be visible, like the two frames on the left. If instead of hitting the key I described above, you were to hit the tall Enter key in the 10-key pad, InDesign defaults to giving a Column Break. Because the text frames I have in my example only have one column-per-frame, the text has nowhere to go in the frame, so it jumps to the next available frame (if you have a text chain), or it goes into overset text (example shown here:)
…if you don't. To complicate things, some keyboards are mapped to use these two keys as I have described, or they could be reversed or the same, so you need to check what you have. If you go to the Type menu and show the hidden characters at the bottom of the menu, you will see whether your paragraphs are separated by a standard return (shown on the left) or a column break (as shown on the right). If you are pasting from another program, your text could have either of these breaks before you paste it. And, you are better off not pasting from another program if you can help it. Save it as a text document and import it.
Another reason might be that InDesign can't display the type because of the way it is set up. For example, you can have InDesign keep some specified number of the lines of a paragraph together, or keep two or more paragraphs in the same text frame, or keep a word from hyphenating (thus forcing it to the next available line in a paragraph—this sometimes happens on a long URL or foreign word that ID doesn't know how to hyphenate), or keeping words of a paragraph together with non-breaking spaces. In any of these cases, InDesign might not be able to display a bit of text in a given frame because of the physical size of the frame.
Check to see if any of these is the cause, and if not, come on back.