have a bunch of letter character else when pressing Alt key + a (bunch) letter
 

What software in the world can give a letter character else when Alt or Shift key + a letter key is pressed for about 13-15 keys?
Up to the point that is creating new input method: a reliable single (right) handed keyboard capability

As for Shift key + letter, the shift function is done by Ctrl+Shift to give/register upper case letter

Please give correct solution

Could you please rephrase your question? I cannot parse it.

That said, ArchWiki has some suggestions re. custom keyboard shortcuts.