first steps into assembler

My knowledge around c++ is poor. Compiling Espruino by myself is out of my knowledge too. Working with assembler is something I will have a fair chance.
Therefore I would like to ask if there is a "not complicated way" to do some of this in assembler

• set values in an array (typed or not, it doesn't care)
  
• return an array
  
• return a string
  
• support call of internal function (old basic version had something like adressOf(spi.send) for that)