Since I think your already old enough to know what are the numbers 1-10, 1 is an equivalent to a singular object or we can so say (only 1 ball for example), 2 is equivalent to double object ( 2 balloons for example), I hope you can guess the rest cause i know your smart enough to know. now let us talk about that plus sign (+), that is an additional sign or we can also call plus sign, as for the word itself you might already know that addition is when you add different numbers together to make a bigger number. so when you add 1 plus (+) 1 it is equivalent to 2. Now there is one more symble that you need to add when doing addition, it is called an equal sign (=) it is used to show that right after adding numbers together the number after that sign means the answer of the numbers you have added.

Hope this helps, have a wonderful day/noon/night and carry on learning. :)