User is prompted to enter their password (and their username) when installing software on Mac OSX.
This is a security measure built into OSX. Most programs copy files to the system Apps folder, which requires elevated permissions. As such, the user is prompted for their login password to confirm that it is them installing the software. This protects against malware and unauthorized users at the keyboard of your computer.
If the user is not an administrator on your Mac, they may need to ask someone who is an administrator to enter their username and password to complete the software installation.
Enter the login password for the account, or if the account is not able to install software, have a user who can install software enter their login information instead.