Folks;
How can i give a user the privilege to upload files into Solaris UNIX box using sftp?

There is nothing special about sftp over ssh access. They need to use a standard UNIX account.

i'm not really familiar with this, how can i do it?

man useradd
man passwd

add a user with "useradd ... <username>"
give them a password with "passwd <username>"

then they can use sftp assuming you have sshd started on the server.

I'm familiar with adding user & give him a passwd. The issue for me is the command this user should use from another machine to upload files into UNIX server.

Thanks for the help

It would help if you told us what the client machine was.

The command "sftp" springs to mind of course.

The clients that user will use to upload his files into the UNIX box are Win & Solaris