Your description seems a bit garbled, but you migt want to see help for
TINV and NORMINV functions.

Jerry

gpktm wrote:

How do I use the Student, x^2 and Gaus (normal) distributions?

For example in student distribution for n samples and error probability
of 5% I'm going to Student's table I'm going in n-1 row and t=95 and
find the corresponding number. But in Excel I don't know how it works.