Hey!
So first, you need to know that one is just a singular thing. Okay? Next, we're going to apply the operation addition. This brings things together to create a new amount!
Assuming we're working in the base 10 number system, the number one and its duplicate combine together under the operation of addition to form a brand new number. We actually call this two! Converting everything back into numerals, we have
1 + 1 = 2.
Hope this helps!