Hi Mabel, keeping hens is easy peasy and the eggs are fantastic (nothing like shop brought ones.)
On the plus side - fantastic eggs, the poo is very good for the garden, they will eat all your slugs and snails, cheap to keep!, very funny to watch and can usually be quite friendly. Can be left to look after themseves for a weekend if you go away.
On the not so good side - they do poo alot (a bit bigger then a golf ball size) and usually quite soft, if they are allowed to roam around the garden, they will wreck it, they dig up everything and eat everything and then crap everywhere!
It really depends on the size of garden you have, my sister has about a third of an acre and they have four hens, but on a garden that size, they don't make too much of an impact. On a smaller garden though, you will notice the damage more!
They don't make too much noise (it's the cockeralls that do that!), just a bit of gentle clucking when they lay an egg (which is understandable 
)
You can feed them pellets/mash, which is fairly easy to get hold of, plus scraps from the kitchen, our chickens love tomatoes, cucumber, fruit cake, marmite on toast and grapes
Have a look at www.omlet.co.uk for ideas on caring for them, they sell fantastic hen houses called egloos (expensive) but there is loads of other helpful bits of advise on there, plus a useful forum.