Wireless G VS Wireless N Router's ( Speed problems)

Can anyone tell me the difference between G and N routers? Also, can you use either one? I currently have a wireless G. I have added A few wi-fi devices in the last couple of weeks I.E. Smart T.V., I-phone, I pad, and Satellite TV ( the on demand comes from the internet). My internet on my laptop seems to have really slowed down, and I it keeps locking up. I have to go reset the modem, and router to get it working again. Could all these wireless devices being on at the same time be dragging down my speed?
Thanks in advance