Sculpture is a fantastic art form which unfortunately isn't as popular as it should be. If you want to give it a go, how do you go about learning it?
The answer isn't as obvious as you might think. I was browsing the sculpture topic on Quora the other day and there was a question on there, sitting unanswered, which I felt needed a reply. The question had been unanswered for some time and asked "how do you learn to sculpt". The problem, is that the question (or perhaps the subject) is too broad. Sculpture as a concept, embodies so many different approaches and mediums and each medium has very different techniques. Sculptures can be made out of stone, wood, metal, resin, plaster, clay, etc, etc and each material has different techniques. Of course, lets not forget more modern conceptual sculpture such as re-presenting found objects (by this I mean, for example, Damian Hirst's 'The Physical Impossibility of Death in the Mind of Someone Living' - A shark in formaldehyde) or even living sculptures, such as Gilbert and George themselves.
The thing is, even when you make up your mind and find a concept or material you would like to explore, learning the skills, to achieve any grand vision you may have, is again not an easy task. Although in art school you get exposed to various techniques within sculpture, if you want to take a less direct route and do this as a hobby or passion, courses are few and far between (certainly here in the UK).
Fish Flow - Alabaster, 2006 I have always been passionate about sculpture, I guess it started in my childhood building things out of Meccano and Lego. Having bypassed art school, I have always been on the lookout for courses to learn new sculpting techniques. I had the opportunity, when living in St Albans, to attend a short course in Stone Carving run by Mo Gardener who gave me the foundations to go out and build on what I learnt. I was lucky, as stone carving courses are like gold dust!
If you are into wood carving, this is a little easier, partly because it seems to be the watercolour of sculpture; a favourite amongst amateurs. Most colleges seem to run wood carving courses in their part-time prospectuses and wood is a great medium to work with. Just check out David Nash for inspiration.
In regards to metal, this is more complex, most casting is done in a foundry so clay and plaster techniques are what you are looking for and these occasionally do crop up in colleges, but failing that get some playdough and, er, play?! Of course, construction sculpture in metal requires very different skills such as annealing and wealding, which again can be learnt at various establishments, you just won't find these listed under the heading Art.
And the list goes on...
So really, the answer to the question is work out what you want to do, then try to narrow down the skills you need to achieve it. Learn from what inspires you, try to get a feel for how a sculpture affects or interacts with it's environment (Anish Kapour is a great one to look at here) and see how form, texture, material, weight, colour, etc can be used to convey your message.
And failing this, you could just use a paper and pencil (or CAD if you want to be flash) to explore your ideas and then get it fabricated for you.