Hi

[#1]

How can i make a distance calculator.like if i have a field named station. so how can i give two selection in stations  ???

[ThornOfCrowns]

That depends on what you've done already. Perhaps two selection boxes with Start / Finish station?

[#3]

Use two variables (if you need to select only one start and one end station) or alternate states (if you need multiselection or you like to recognize how alternate states work) ....