First off, even if you go the wrong way when following a satnav or signs in the independent drive section of the test, provided you go the wrong way correctly there is no fault. If you end up in a lane that's left turn only, mirrors, signal and go left. Do not try and correct a mistake (e.g. you should have been going straight ahead). The examiner or satnav will re-route to get you back on track.
The satnav used in the driving test is a TomTom - the directions are clear enough although sometimes does have some quirks like "cross the roundabout, 2nd exit" when the 2nd exit is more like 2pm. It will give directions in advance based on speed, e.g. in 300 yards turn left, then as you get closer to the junction it will repeat the direction for you. So you're getting more information than you would from your instructor or examiner.
Most of the time it is obvious and if there's some doubt then the examiner will clarify the direction to go. For example, there's a roundabout here where the satnav says take the 4th exit, the signs and instructors always tell pupils take the 3rd exit so examiners jump in with the direction to go.
It will sometimes chain directions together - e.g. cross the roundabout 2nd exit and then turn left. You might think by that it's an immediate left turn, but if you glance at the satnav screen you might see the left turn is 300+ yards away. Again examiner will normally clarify this.
Use the satnav by listening to the directions and GLANCING at the screen - the top row will show the direction you're going and the distance to that direction. Do not stare at the satnav as you will likely drift out of lane.
As said above, it isn't rocket science.
Also remember 1 in 5 tests are still asked to follow road signs for the independent drive. My experience is much more - 50% of tests have been following signs instead of satnav. Just luck though, and you should have more probability of being asked to follow the satnav directions.