What are and How do Texting Apps work?

I recently just got a iphone but my parents didn't get me a texting plan(a phone w.o texting ikr) so basically they told me to just use a texting app since everyone has a smart phone now. I don't really get exactly what it really is, does it give you a number that people text you with, or it like Skype were everyone i want to text has to have the app too. If any of you have great wisdom to shine on me with ti would be greatly appreciated

It is just like iPhone texting except runs off the internet. If you have 3g it will run off of that and if you are in Wi-Fi it runs off that. If you don't have 3g then you need Wi-Fi. It will assign you a number and thats what you will give out to friends.

Most texting apps require a texting plan because they just add features to the default texting app.

Other "chat" apps send messages using your data plan as opposed to the regular way. These require you to register a nickname similar to skype.