Here is some basic C# for creating a new tag:

var newTag = new TagInfo();
newTag.Name = "Tag to create";
newTag.Description = "Description of new tag";
newTag.IsSecure = true;

bool autoRenameTag = true;
Tag.Create(newTag,autoRenameTag,RASession);

If you check the LF Administration Console after running this you'll see this:

There are other options for modifying other tag settings (see below), so the above code is a good starting point if nothing else.