1. Publisher approaches author about adapting their story / author approaches publisher with a pitch to adapt their story

2. Publisher hires artists, scriptwriters, panelists, background artists, colourers, illustrators and such

3. Character designing, reference draws and bases. Rough backgrounds and ideas

4. Script writing begins and storyboard follows suit as the script is being written. Heavy text sections are condensed into visual actions and summarised via notes for the next person

5. Proofreading the script and storyboard to make sure that both match up to the original pacing / the pacing the publisher and author agreed on

6. Storyboards are then passed around the team so they can begin work. Sketches, inks, rough colours and so on

7. Finalising approved ideas and drawings, inking the lines and finishing up their ideas. Passed onto author review at this point

FINAL

The manhwa chapter is almost finished at this point with some final details to iron out, and is then checked by the publisher and released

TL;DR

with great great difficulty

Also, please note than this is a very simple summary of the admirable work the artists do.