How would i get the highest number from this?

Your title says that you want to get highest number, for that you can use math.max, it returns highest value from given values. Example:

math.max(10, 5, 200) -- 200
math.max(0, 1, 2, 3, 4) -- 4
math.max(-50, 10, 500, 25, 300) -- 500

In your case you have table but it does not accept tables, you can fix it with unpack. It turns table into values that it returns it as a tuple, it only returns values that have index as a number (In your case you don't need to worry). So you could do:

local Highest = math.max(unpack(Coins))

This will return the highest value from that table, the problem is that you said you want them to be in order like 1st, 2nd... so here you should use table.sort! It sorts the table by using basic loop by given function. It accepts 2 arguments, the table itself and function, the function in your case does not have to be included because it automatically assigns the < operator it. In your case it would look like this:

local Coins = { 1656343636363, 2000363646, 35462564642, 43587385730, 37504757030}

table.sort(Coins)

It runs loop for every element which then picks random other element from the table and since i did not put any function there, it uses as i said < operator so this would sort the table from lowest to highest so the result would be:

[1] = 2000363646,
[2] = 35462564642,
[3] = 37504757030,
[4] = 43587385730,
[5] = 1656343636363

But if you want it to sort from highest to lowest, you would have to make the custom function in argument 2. All you have to do is swap < with > and it will be done:

local Coins = { 1656343636363, 2000363646, 35462564642, 43587385730, 37504757030}

local function Sort(Number1, Number2)
    return Number1 > Number2
end

table.sort(Coins, Sort)

The Number1 and Number2 are the random keys from the table it returns, you must use return because it returns bool value and if the value is true then it will sort the Number2 above Number1's index while if it is false then it will sort it below the Number1's index, this should return:

[1] = 1656343636363,
[2] = 43587385730,
[3] = 37504757030,
[4] = 35462564642,
[5] = 2000363646