what do i use it for? say i go on vacation to another country and want to use another sim card? im not sure how to get one from another country. do i have to actually sign up for a plan there

They usually have pre-paid SIM cards at the airport when you land.
Shouldn't be hard to find them.

and does it work like by the minute? do you sign up for a service for a week or so and then pay for it at the end or something?

They are PRE-PAID. You buy them with with a preset amount of money on them. Like a gift card. As you use them, the amount decreases. They are ALWAYS very easy to refill or "top up".

All you will have is voice and SMS text and they normally do not have data, and they very rarely have BlackBerry Data.

(nm)