'ain't' is a contraction of any of the following:
am not, is not, are not, have not, or has not
"I ain't able of that" is wrong., because you can't say ' able of ' ,you either say 'able to' or 'capable of' and both have the same meaning then.
" I ain't capable of that."or " I ain't able to do that."
( In both cases 'ain't ' is a contraction of ' am not'
Other examples of how to use 'ain't;"
- He ain't ready for it ( contraction for 'is not')
- They ain't got any money yet ( contraction for 'have not')
'ain't' is a nonstandard word!