This is done somewhat commonly, especially by new users of Mathematica. Elements of a list are indexed using double square brackets: [[...]]. Functions are given their arguments with single arguments: [...].  So what is essentially happening here is that a function called solc is being defined. It is being defined to take the whole numbers 1 thru 8 and return the values you see. Both of these work of course as you saw.

I myself would normally define solc to be a list like this:
You can then acces their elements with the list syntax such as solc[[1]] or solc[[4]].

Hi,

Assignments like f[0] = 10 can be made any time. All occurrences of f[0] will then be replaced with its value, 10. The argument can be any Mathematica expression, so f[0.1] = 10 and f[g+h] = 10 are also possible.

In contrast, in order to be able to make an assignment like a[[1]] = 10, the list a must have been allocated beforehand, e.g., using a = ConstantArray[0,10], a = Range[10] or a = Table[0, {10}]. The index in the double brackets must be an integer and the corresponding element is replaced with the value. Note that a[[0]] is the head of a, i.e., List.

Youngjoo Chung