No worry about messing up settings as the inbuilt programmes are in memory so experiment as much as you like.
Take care with learn accept and reject. You can have hundreds of notches with the Spectrums so could take out every size and shape of ring pull but as Ernie says gold rings and ringpulls show up at the same places so its best to accept that you will have to dig some.
Do select a tone that suits your hearing right from the start. It can make a lot of difference.
I never use icons as it slows the machine down and they are not reliable. Use numbers as a guide but the bars on the display are the best feature as you in effect have target sizing like the top Garretts and two items of in the same hole can show bars in different parts of the display while the I.D. number will just add the two together and give the wrong answer.
Learn the shortcuts i.e. if your adjusting anything, sensitivity, volume, tone etc then you can just press an arrow key and it takes you back to the last adjustment made so you can tweak up and down in seconds without having to plough through menus.
Up the DC (non-motion) sensitivity much and the excellent pinpointing goes out the window. Use pre-amp gain to gain all metal depth, then you won't have that problem. You can use V.C.O. pinpointing but with normal mode its easier to trace out the size/shape of larger items to help deside whether they are worth digging.