Guppies are such pretty little things. . . first, I'd like to point out that names shaded in grey (such as Guppy
in your post) will link you to our tropical fish profiles, where I'm sure most of your questions would be answered. You can also get there by clicking on the link in the toolbar above.
Guppies are social little creatures. Though they aren't considered a shoaling fish, in my experience, guppies will be happier if they're kept in a group of at least three - they *can* get a little bit reclusive when kept alone, but that seems to depend on the fish. . .some don't seem to mind. The minimum recommended tank size is 5 gallons, which would probably be okay for a single specimen, but these guys are active when they're happy, so I personally wouldn't keep them in anything less than 10 gallons of water. Best if the tank is longer than tall, they appreciate the swimming room.
You can keep males together, but they can be nippy with each-other - or not, it does seem to depend on the temperament of the individual fish. You'll want to keep an eye out for any bullies in the group, though.
Guppies are really easy little fish to keep, they don't have any special requirements (that I know of) as far as the tank is concerned. They'll appreciate the cover of plants, (real or fake) and being curious creatures by nature, they'll 'explore' any tank ornaments you put in for them. If you do
get more than one male, I'd highly recommend that you be sure to give them plants/decorations/places to hide - so they can
get away from one another if bothered. This will help keep any possible aggression to a minimum.
Feeding is also easy, a quality flake food will keep them in good health. Livebearers love their veggies, so you can toss in a bit of a pea (softened and squished) from time to time, and they also appreciate the occasional 'meaty' treat, like brine shrimp.
I hope this helps, and welcome to the forum!
EDIT: just saw you're from the UK? Google tells me that a 10 gallon tank is 37.8 liters, and a 5 gallon is 18.9L :)