How do I use RESTful apis from Unity?

RESTful API's seem quite common these days for many types of web based services, but I can't find any 'beginners' tutorials on how to use a REST API within Unity. Personally I am trying to access an SMS/MMS texting service from Unity but I'm basically having to guess what to do, as their documentation presumes I know 90% what I'm doing (They are about 1% right). Searching for things like REST on the wiki often offers no help at all (especially when wanting to use this in conjunction with Unity). I know this is a broad question, but pointers to tutorials would probably be a good start to help myself and other beginners.

Thanks!