Difference between print() and println()

An easy way to see the difference is using Serial.print();/Serial.println();.

print();

will print out whatever you input wherever the cursor currently is. For example:

Serial.print("Test");
Serial.print("Words");

This will print:

TestWords_

The underscore marks where the cursor is (and therefore where the next print command will start). In contrast, the code:

Serial.println("Test");
Serial.println("Words");

will print the following:

Test
Words
_

You can also print multiple statements and then follow with println like so (note the space at the end/beginning of the strings):

Serial.print("These ");
Serial.print("Test");
Serial.println(" Words.");

to get the following output:

These Test Words.
_

You can also use println(); to add a newline character in general. If you would print a variable that doesn't return a newline character, println(); can be used for formatting. Example:

int x = 50;
Serial.print(x);
Serial.println();

This will print:

50
_

Finally, you can add in special characters like a tab \t inside your quotes for formatting. Example:

Serial.println("Test\tTest")

This will return:

Test    Test
_

print() prints whatever you send in.
println() does the same thing, only after using println, anything new that is printed gets printed in next line, I.e. a new line is formed.