Where is the way to learn lua fast
The only way to "learn lua fast" is if you already have knowledge of programming in general in such a way that you can apply the same logic from one language to another. Programming languages, like Lua here, tend to use english words for most logical operations - like flow control, loops, variable definition, among others - which makes learning a new language through applying what you already know from another language pretty straightforward.
If you don't have that experience already, there is no "fast" way available to you. You have to do it the normal way that everyone had to go through: Learning it normally.
SRB2 is going nowhere and this isn't a race. Take your time, don't rush.
There are plenty of Lua resources out there, some good, some bad, but you won't learn anything if you don't just get to it and experiment!
Seriously.
There are a lot of resources. Pick one and try it out. If it doesn't work out for you, try another.
It works better if you have some place to play around with the language. If you're experimenting with vanilla Lua, you can try one of the many online Lua interpreters out there.
lua.org offers a few.