Since your relay is a SPST, only 4 leads are used - the fifth lead probably has no connection. Since you are puzzled, I will assume the relay is in a sealed box, you can't see inside, and there is no manufacturer's name, part number, or data sheet.
To identify which leads go where, you will need an ohmmeter. Connect the first ohmmeter wire to one of the relay leads. Connect the second meter wire to any other relay lead - notice the reading. Move the second meter lead to another relay lead - notice the reading here. Continue with the process untill you have identified two relay wires with a resistance in the range of 50 - 1,000 ohms (these are the coil wires).
Attach the coil wires (identified above) to a suitable power source (5 volts DC?). Of the three remaining (unused) relay wires, two will have 0 resistance when the coil is powered-up and infinate resistance when the coil is not powered-up - these are your switch wires.
(2) I like to use diodes whenever I use relays.
(3) I am guessing that 5v means that the relay has a 5 volt coil.