Is there any website(s) to look up words with similar pronunciation or spelling?
For example: stack, steak, stake, stick.
(It can help me as a non-native English speaker to learn confusing words.)
You're describing homographs, words which are spelled the same way but which mean different things and may be pronounced differently (fore example moped,) and homophones, words which sound alike but mean different things and may or may not be spelled the same way (for example away and aweigh.)
There's no search engine for those that I am aware of or could find in Google. There are, however, many lists of these types of words on the internet, such this one.