It's better to turn off the wifi and any other apps that you don't use before every gig, because it gives the cpu more power on the software and you don't have to worry about lags and audio dropouts.
About analyzing files, serato sometimes doesn't get the bpm correctly and if you want to find out the real bpm of the track search for it on beatport, or songbpm.com or just use an app like tap tempo and discover it yourself. That's why I beat match by ear even though I'm using mixtrack pro 3.
Hope this will help you. ;)

Using the auto will work most of the time but will sometimes double or halve the BPM of certain songs. You use the ranges to fix those tracks. For example, if you're scanning a folder of Dubstep, set the range low so they don't all show up as 140bpm.
To start analyzing I believe you can just click the analyze button to start doing all tracks. Otherwise just drag the tracks you want to be analyzed onto the button.

so in the mean time i have found the answer that one has to turn of the wiifi to anyalyse files so thats all good now.sorry if i seem a bit dumb with this just learning how it all works.with the bpm when i click it on there are numbers one can set there is the word none then numbers under that so its that bit which is tricky.what numbers do we click on cause wouldnt each song be different if one is analyzing serveral songs at once what do we set it at.

or shall we leave it at none and change the bpm manually

well for a start wifi has nothing to do with analising tracks or bpm so where ever you got that notion from it's wrong.

there is a tick box that says set auto bpm, tick that if you want the bpm to be saved when analising tracks,

and range is as it says, a range you want or know the bpm to be, for example if i'm analising drum and bass tracks that i know will be in the 160-190 bpm range i would set it to 98-195 so the software will not detect the tracks at half beat and set a 180bpm track as 90bpm,

if you are analising a mixture of tracks from multiple different genres then you would set the range as none as you dont know what the bpms are, but don't be surprised if it gets a few wrong, for example dupstep tracks often get marked as 140 but to me i would class them as 70 bpm so the software will mark some as 70 and some as 140, but if i was to set the range 58-115 then they would all be marked in the 70 range,

as you will most likely be scanning top 40 chart music i would just recommend setting it as none and manually fix the ones it gets wrong

Or just reanalyze the wrong ones with the proper range selected.

i dont have a tick box.next to the analyze is a drop down box it has the worrd none then a group of numbers to select.so i dont know where the auto is.so is it ok to leave it at none and change manually as needed.