I think you will find this tutorial very helpful https://compasstech.com.au/TNS_Authoring/Scripting/lua_tutorials.html. Of course you can also look at the official documentation, but I think that without any prior experience, just reading the docs can be a bit daunting. You should know though, that Lua by default has no way to handle graphics, so for whatever testing you may want to do, you will either have to do it on your calculator, or on the computer app. You may also want to install an on-calc IDE. I personally like Jens Lua IDE
PS: I was shocked to find that ndless-apps.org is no longer operational : (
It's such a shame, because it's largely because of it that I became so interested in scripting and low level programming for embedded systems...