Use of AltGr key in UK keyboards?

What is the use of AltGr key in UK computer keyboards? I only found that they are used to print € character. What are its other use? Why UK keyboards have Alt and AltGr keys instead of two Alt keys?

Thanks.

It is for all the accented type characters - for example ALT-GR + E = é etc...

Any other uses? It also performs some weird things while pressed with some other key in Word 97/2000.

Like AltGr+N = change page layout.
AltGr+M = add comment etc.

Is there any way to change AltGr functionality same as Alt key? I tried to change keyboard type from UK to US in control panel. But it didn't solve the problem.

Any help is welcome.