I will omit the hyphen. Please wait for one second. One second is one sixtieth of a minute. 1/2 is one half

examples

You might use it if someone asks you to do something and you cannot respond straight away. If i was writing something and someone asked me a question i might say "one second" as a way to get them to wait whilst i finished what i was doing. Some would say "one minute". Its really shorthand for "wait a second, or wait a minute".

When do you use it. Please would you give a couple of samples?