So what you guys are doing is your not actually making a logical adder. The creator of this post made exact predetermined solutions. This is only possible because he used small numbers and therefore there wasnt that much to code for.

You want to make an adder. Wikipedia offers a good tutorial. However note that wikipedia also literally gets it wrong. The logic diagrams are wrong. Just google around and you will find some good tutorials. For each bit you will need 6 logic gates. I think it is something like 3 xor 2 or and 1 AND. I cant remember. Carrying is easy. Just make sure to use carry full adders.

I suggest using binary, performing the calculations then converting back to a readable output. Converting binary to 7 segment is amazingly difficult, so don't focus on that until you have alot of background information on what you are trying to achieve.

I don't really understand how to use it. Needs instructions.

A simple binary adder can be created by making a grid of xor gates with a carry (if there are two inputs then you shift the output to the left). With the binary to base ten thing, you need to (this is from Massey101 and it is the best way I can think of) put metal across and fill in PSCN in the middle and when you want the metal coming across (the binary input) you have NTCT but when the number (base ten(up)) is not one that you want with the binary you have to have PTCT. If you create it correctly it works really well.