I'm going to 'name and shame' Pigmini here. She got me into this fine mess!!!!
Sue told me about Mochila bags and of course my nosiness got the better of me so I had to go and look. There are quite a few links on Google to help you with more research and there's a great group on Facebook who have been very helpful - along with Pigmini too.
The technique is tapestry crochet and involves 'just' the double crochet (or single if you're American). Easy you'd think but it isn't!!! The number of times I started and pulled it out just to 'get' the base done was beyond a joke!!!
Before I could start I had to choose some yarn. It can only be a cotton yarn as others just don't work. You can see my collection in the top picture. The other three pictures are from one of my many 'bad starts' and all got pulled out so I could start again. I can be so stubborn over learning new skills. Thankfully the Facebook group are really helpful and in their files section are some useful links and some terrific videos.