Objective C - basic knowledge

I would like to understand and elaborate on the code posted in GitHub about the Romo robot. It was mostly written in Objective C, which came before Swift. What are some good resources for learning enough about it to encapsulate into new code?
Thanks

Here is an alternative. Why not try this site to convert the Objective C code to Swift?

https://swiftify.com/converter/code/

Hmmmm, seems to be limited without a paid subscription.