In Windows 10 tablet mode:
To select text to highlight, I just touch and drag across the letters I want highlighted.
Or to quick select one word, touch that word to highlight it.
To Copy, touch and hold the highlighted area until a box appears and select Copy from the options.
To Paste, touch an area and hold, then choose Paste from the options.
There is no other magic way I know of to make it faster than this, unless you connect a mouse.
Let me know if there is anything else I can help with.