Is it easy for people to steal someone else's passwords?

The ease or difficulty depends almost entirely on two factors: (1) the ease with which the server containing the relevant passwords can be hacked, i.e. if you want Jane's Amazon password, this metric would concern the difficulty of hacking into Amazon, and (2) the ease with which the individual computer where the password is used can be breached, i.e. access to Jane's computer. The third most important factor, but it is distant, is the simplicity of the password. Passwords like bu6iFL5apgt70pXa are much harder to crack than 123456.

However, hacking is a crime in almost every country and should not be performed. This answer is only to demonstrate the ease or difficulty of performing such an activity.