2.25 explain some uses of electrostatic charges, eg in photocopiers and inkjet printers.

Inkjet Printer

In an inkjet printer tiny droplets of ink are fired out of a nozzle and onto a piece of paper. To control where these droplets go the droplets are negatively charged as they come out of the nozzle. They are then passed through two plates which each have a charge. The charge in these plates is varied so that the droplets are attracted or repelled by a certain amount thus giving you your printing on paper.

Photocopier

An image of what you are copying is projected (with light) onto a positively charged image plate. Whiter bits of the image makes the charge leak away in those places. These charged bits then attract negatively charged ink powder. A piece of positive paper attracts the powder instead of the plate so the image is printed onto the paper. Heated rollers heat the plate up so the powder sticks.

2.24 explain the potential dangers of electrostatic charges, eg when fuelling aircraft and tankers

Lightning

As the rain drops and water vapour bumps together static electricity is created. This leaves the top of the cloud positively charged and the bottom of the cloud negatively charged. This creates a huge voltage (charge difference) and a big spark to earth.

Fuelling

If you're fueling an aircraft or a car the fuel rushing out of the pipe can cause static to be created. This can easily lead to a spark which can ignite the fuel. To prevent this make the nozzle out of metal so that the charge is conducted away. Also earthing strips are necessary to discharge the static safely.

2.23 explain electrostatic phenomena in terms of the movement of electrons

As the difference in charges builds up so does the voltage.
If enough electrons have moved  so that the charge difference is great a spark can jump from one side to the other.
It's all about the movement of electrons. 

2.22 understand that there are forces of attraction between unlike charges and forces of repulsion between like charges

Like forces attract
Unlike forces repel
e.g.
+ repels +
- repels -
+ attracts -

2.21 explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons

A build up in static charge is caused by the movement of electrons. Only the electrons move. 

A positive charge is caused by a loss of electrons.

A negative charge is caused by a gain in electrons.

2.20 describe experiments to investigate how insulating materials can be charged by friction

Static Electricity

Take a rod of plastic such as acetate or polythene and rub a cloth duster against them. This builds up static charge. Then take a positively charged material and tie it to a string so its suspended at the halfway line. Take the plastic rod and place it near to this material. If the rod is positive it will repel and if it's negative then it will attract.