login-logout in asp.net with c#

Question

hiii....
m creating my first website which inluding some of features...
there in master page which has login link.on click login link login.aspx will be open.
here in my problem..
after clicking login link the text should be logout.
where to write the code for it.
used cookies,session for it but not working propely..
can anyone give the code example..?
help me.
thanks in advance..