Need geek help for mobile internet on a laptop

Kidsandliz thought this was worth mentioning said
1

I have a several years old Mac Air. I need to get one of those things you plug into the computer that gets internet when you are traveling (eg the modem hardware) to use when I am where there is no internet, etc. I also need suggestions for which service to buy to get the service from. I am not sure if this is going to be the solution to my problem (having internet in a variety of locations - and no I don't have a smart phone and a smart phone won't work well for teaching online) but I also know I don't know enough about it to make an informed choice. Thanks all.