First time ask login details,Again run not asking login deta

Question

Thank you,I am running the project immoderately asking userid and pwd i am enter the details its checking backed database  it's correct disply that corresponding some another page,it's wrong display error msg.

My question is ia m running the first time asking login details ok,I am  running second time not asking again login details automatically display that corresponding page,

can you give me one simple example on this plz help me what concept is involved to do this?????