Get yourself a book "Python Crash Course 2nd Edition", read it with Nim tutorial part 1, And Nim for Python programmers from Nim Wiki on github. Translate yourself code from Python and write it as Nim, there are some differences but it's really easy to spot them. And of course do the exercises from the book. They are the most valuable.
And the last thing - read runnable examples from modules in Nim stdlib. They have nim snippets that are ready to run and use.
