Following piece of code creates a group named "Regions" and adds a Term Set with name "Asia" and India, Afghanistan and Pakistan as terms inside Asia Term set.
using (SPSite site = new SPSite("http://intranet.contoso.com"))
{
TaxonomySession session = new TaxonomySession(site);
TermStore store = session.TermStores[0];
Group group = store.CreateGroup("Regions");
TermSet ts = group.CreateTermSet("Asia");
ts.CreateTerm("India",1033);
ts.CreateTerm("Afghanistan",1033);
ts.CreateTerm("Pakistan",1033);
store.CommitAll();
}