iPhone 5 Data Usage Question?

[lalaland]

so today i just got the iphone 5. my plan only has 100mb of data with it. the lady told me not to use the mail app, since receiving new mail will use data. so i havent set up my mail app, and won't plan on doing it. i also am planning on only using Wifi at home and school, and not using data when there is no hotspot (so i wont surf the net, watch videos, download apps, go on app w/ internet when i have no wifi) but i may need to look up some stuff here and there for the odd reason when i have no hotspot, so then i would be using my data. But for the apps, i was wondering if i have to sign out of them everytime? i pretty much turned off ALL notifications for all my internet apps in general(facebook, instagram etc) so i only get text and phone notifications calls etc. but do i have to log out of facebook and instagram everytime after i use? if i leave it running will it use data? should i end all multitasking on my phonee? i dont wanna use up my data since i dont have alot, and was wondering if everything i'm doing is good, and will not use up my 100mb of data? thanks.

[Chiko]

damn 100mb is too little, go to your setting and turn off 3g and 4g and only leave date on so you have the lowest speed activated and that wont make it go by too fast
you donnot need to log out of anything and you can activate your email whenever you want
make sure you go to setting>general>network and turn off data.
you can also see how many data you had used by going to setting>general>data usage
once again it seems pretty obvious that you are new to iphones but just make sure you have data off everytime until u need to use it