Your relay is whats called a SPST or single pole single throw, meaning it has one pole (switch) and one set of contacts.
One terminal is the input and the other is the output. Doesnot matter which ic wich so take the black wire from the pump and the black from the power supply and connect them togeather.
Then put the red from the pump under one relay terminal and the red from the power supply under the other.
When you activate the relay the switch will close and the pump will run. Viola!
Daz