I'd love to volunteer

If you're a practical person, I'm assuming you'd like to get involved in work parties doing maintenance work and the like. Whilst there is a "Job search" facility ( www.rspb.org.uk/.../ ) for volunteer roles on the main RSPB website, in your case it's probably best to simply talk to your local reserve and see what they suggest. Many reserves have regular work party days which are a good way to get involved before perhaps picking up more specialist roles. A quick search of Oxford gives the Otmoor reserve, but there may be others closer to you www.rspb.org.uk/.../