First off, I hope it is not annoying to ask more than one question in a thread.
1. In my mother tongue, these two words are almost exchangeable, so the dictionary gives out the same result. And I had been only using "can" until a message popped out from my computer, it said: You may eject the device now.
I heard that "may" is used in giving permission context, and "can"is used in describing ability context. So is this sentence completely incorrect for using "can"? And I should use "may"?
Walkers can cross the road when the traffic light is green.
2. My teacher told me to use "to" when the sentence contains two verbs, but what if there are more than two verbs? Like "I decided to go to the food stand to buy something to eat?" I find it has too many "to", Is that correct?
Many thanks in advance.
For number 1, may and can originally had different uses, and some grammar books will tell you that they are different.
However, most native speakers use "can" for both purposes.
"May" is used to ask permission in a more formal way. In other cases, "may" often means "maybe" or "might".
1. Can I go to the store? - Simple asking of permission
2. May I go to the store? - A more formal way of asking permission
3. He can go home. - He is able to go home.
4. He may go home. - He MIGHT go home.
My suggestion is to just stick with "can", unless you want to ask something formally or mean "maybe" or "might".
For number 2, the sentence is correct. You can use multiple verbs like that.
Hope this helps
You'll get quicker answers that way as many people could answer one of the questions but may not have the time nor knowledge to answer more.
Additionally, when different people choose to answer different questions the thread becomes cluttered and confusing.
The person who wrote this message - it being Microsoft code - was probably brought up on Strunk & White. Probably his English teacher, Mrs Thistlebottom, would have said 'Of course you can remove, it's only a memory stick, and a USB port's friction isn't that hard to overcome!' (except that Mrs T probably wouldn't have used an exclamation mark there). The point is that Windows gives the user permission to remove it (and implies that terrible things will happen if you just do it without asking first).
In a life spent working with these people, I'm afraid that I've noticed a strong correlation between software engineering and grammar tyranny.
I prefer machines that indicate something is possible, rather than ones that grant me permission.