You won't be able to connect the nowtv stick to your Talk Talk box because the HDMI port on the Talk Talk box is an output port and not an input port, so it won't work
I am assuming you have bought the stick because either you have an older Talk Talk box and the NowTV App is no longer supported or you need the new stick for watching entertainment, kids, Hayu or sports ?
If your older TV doesn't have a HDMI port, then look at a HDMI to Scart or RCA adapter from places like Amazon or Ebay (can't guarantee they will work with the stick and the picture quailty will be down converted to SD 576p or 480p).
Would have also suggested the white nowtv box with the optional RCA cable for older non HDMI TV's where these boxes are now long in the tooth nowadays where some of the newer Apps are not supported due to lack of processing power, so personally i wouldn't go down that route.
If it was me and you don't want to spend much money on a brand new TV, then i would look at a cheap second hand television with a HDMI port from places like Gumtree, where you can pick up some cheap bargains where previous owners are up grading to 4K.