Creating Keyword Term in SharePoint 2010 progrmatically

Managed Metadata is a new feature introduced in SharePoint 2010. It allows you to define terms in a hierarchical collection centrally, and create a managed metadata field that is reference a term sets.

By using the Term Store Management Tool found in Managed Metadata Service, you can create a term set either manually, or by importing a CSV file. You can also create a term set programmatically, either by a feature receiver or a console application.

Now the below code will let you to create a new Term in Keywordstermset and this term can be added as Tag to the Page or Item.
(Check inline comments for more details)

 

                                   using (SPSite oSite = new SPSite(webURL))
                                    {
                                        using (SPWeb web = oSite.OpenWeb())
                                        {
                                            //Get the Service Context of the current Site 
                                            SPServiceContext context = SPServiceContext.GetContext(oSite);

                                            //Get the Social Manager application configured to the current Site Context
                                            SocialTagManager socialTagManager = new SocialTagManager(context);

                                            //Get the UserProfile Manager application configured to the current Site Context
                                            UserProfileManager profileManager = new UserProfileManager(context);

                                           
                                            TaxonomySession taxSession = socialTagManager.TaxonomySession;

                                            //Get the Default keywords TermStore, to which the new Term is going to be created
                                            TermStore termStore = taxSession.DefaultKeywordsTermStore;
                                            // Check whether the term "I am Following" is already exists in the Term Store

                                            TermCollection myTermColl = termStore.KeywordsTermSet.GetTerms("I am Following", true);
                                            Term myTerm;

                                            // If the Count is greater than 0, requested term is already exists in Term Store
                                            if (myTermColl.Count == 0)
                                            {
                                                //Creates a New Term to the TermStore.
                                                myTerm = termStore.KeywordsTermSet.CreateTerm("I am Following", termStore.DefaultLanguage);
                                                termStore.CommitAll();
                                            }
                                            else
                                            {
                                                myTerm = myTermColl[0];
                                            }


                                            SPList lstDiscussion = web.Lists[txtListName.Text];
                                            SPListItem item = lstDiscussion.GetItemById(Convert.ToInt32(txtID.Text));
                                            Uri itemUri = new Uri(web.Url + "/" + item.Url);

                                            if (((LinkButton)e.CommandSource).Text.ToLower() == "follow")
                                            {
                                                //Add a Tag to the List Item with the above retrieved Term.
                                                socialTagManager.AddTag(itemUri, myTerm);
                                                ((LinkButton)e.CommandSource).Text = "UnFollow";
                                            }

                                            else
                                            {
                                                //Delete the Tag to the List Item with the above retrieved Term.
                                                socialTagManager.DeleteTag(itemUri, myTerm);
                                                ((LinkButton)e.CommandSource).Text = "Follow";
                                            }
                                        }
                                    }