Not at all Colin place the symbols in a triangle, W (watts) on top, V (volts) and I (amps) on the bottom read as follows W=VxI, V=W/I, I=W/V same sort of things for Ohms Law, Volts, Anps and Ohms V on top, I & R (ohms) on the bottom V= IxR, I=V/R, R=V/I; do you want the resistance colour code too?
Say you have an electric device, Kettle, Fire or ---? you want to know what size fuse to use, Kettle 3KW (3,000 Johns) supply voltage 250 volts 3000/250 = 12 so a 13 amp fuse is closest usually available in UK, small electric fire say 1Kw 1000/250 =4 so a 5 amp should do the job.