Writing a number on a line of its own (not part of a larger sentence or expression) is a shorthand for d20 + that number.

For example, if you have +2 to hit with a sword you can type 2 to attack with it.

You can optionally add a + or a -, and also a h or an l before or after the number for advantage or disadvantage.

You can also add an e followed by a DC.