Greetings from London.
You need to connect a line to A1 and a neutral to A2. Connect B1 to A1 so that the cycling starts when power is present.
Then you need to select timer mode B or 2 (C or 3) which is cyclic off/on. If you power up the timer you can now adjust the time on (viz T-On) and time off (viz T-off). You will be able to observe the timer cycling on/off by the little light bottom right. Once you have your desired timing cycle you must carefully turn off and isolate all electricity before the next step.
https://docs.rs-online.com/a392/0900766b810ef473.pdf
To control the pump you need a line wire from A1 to go to terminal 15; the pump line is connected to 18. The pump neutral is connected to A2. Don't forget the earth to the pump.
Now power up again and your pump should be controlled as you want.
I would remark that 1 min on and 5 min off is a switching rate of once every six minutes - does it need to be this frequent? Could you reduce the switching rate and keep the same on to off ratio by say 10 mins on on 50mins off? The advantage would be less stress on both the switch contacts and the motor.
The next important consideration is whether the timer contacts are suited to switching the motor. What kind of motor is it and what is its power rating? You may have to use the timer to operate a motor contactor which then controls the power to the motor.
Finally, electricity and water is a risky mix so I advise you at the very least to employ an electrician to inspect and test what you have done especially that everything is indeed earthed correctly - better to be safe than sorry.
If you post some pictures of your wiring and settings then I can check these - you still call in an electrician though to do the I & T.
