Some time many of us get stuck in providing permission to folder usr/bin, for this first you need to go to the folder to provide permission.
We can find this folder by following steps:-
1. Open Finder
2. From menu bar Select Go to folder option
3. Type /usr/bin
4. Press Go.
5. Right Click on usr or bin folder select Get info
6. In Sharing & Permission click permission lock icon in bottom right corner
7. Enter your Mac password and set permissions Read & Write.