What he did here by C#

Question

string connectionString = GetConnectionString(); ConnectToData(connectionString);

Answer 1

This is what is happening based on the information you have given us:

A string called connectionString is being set the value of a function that returns a string, called getConnectionString.

We then call the function ConnectToData and pass the string we had (connectionString) as it's arguments.
Those functions could be anything, including nothing.

If this is not what you were looking for as an answer, please think about whether or not you have given enough information for the reader to be able to answer your question.

I also see no use in the string, you'd might as well just write:
connectToData(getConnectionString());

Answer 2

There is no function written in what you wrote, but you certainlly call one from somewhere.
That's what functionName(); means. Your just calling that function. Idk what it does, it's not in the code you gave us.

Answer 3

where is the function here