Can i use a 2 string to perfom and addition of their values?

Answer 1

yes, exist the concat method:
string s1="hello";
string s2="world";
string s3="";
s3=string.Concat(s1,s2);

Answer 2

Yes, that is called concatenation. For example:
string s1 = "Hello ";
string s2 = "World";
Console.Write(s1+s2);

Answer 3

yes

Answer 4

string a = "z";
string b = "q";
string c = "";
c = a + b;
//c = "zq"

Answer 5

yes