print and println

System.out.println prints its text and then ends the line, so the next output starts on a new line. Its sibling System.out.print prints the text and stays on the same line, so the next output continues right after it.

System.out.print("Loading");
System.out.print("...");
System.out.println(" done");
System.out.println("Next line");

Loading... done
Next line

print never adds a space by itself. The space before done is there because it is inside the quotes.

An empty line

System.out.println() with nothing between the parentheses prints nothing and ends the line. That gives an empty line, or finishes a line that print started.

System.out.println("First paragraph.");
System.out.println();
System.out.println("Second paragraph.");

First paragraph.

Second paragraph.