How to select a HTML tag

There is no special shortcut to select a tag. HE generic editor, and not specified for any language (this would change with 1.50, where specialization will come with help of plugins and scripts).

But you can use command Edit.ExpandSelection (Edit→Selection→Expand). This is smart function that guess, what user want to select and increase selection range from current to larger one. The functionality is also callable with with double/triple etc clicks (number of clicks correspond to number of calls for ExpandSelection).

The opposite to Edit.ExpandSelection is command Edit.ShrinkSelection, which decrease selection to previous selection scope.