If you need to put someone on hold for another person, the best way to do it is to transfer the call. This can be done by pressing the transfer button on your phone, or by dialing a specific code that will transfer the call. If you don't have a transfer button, you can usually still transfer the call by dialing *2.
When you press the transfer button (or dial *2), you will be prompted to enter the extension of the person you wish to transfer the call to. Once you've entered the extension, press Dial or Send. The caller will then be placed on hold and will hear music (or silence) until the other party answers.
It's important to note that not all phone systems work in exactly this way - some may require you to dial a different code in order to transfer calls, while others may not have a transfer button at all. However, in most cases, transferring a call is relatively simple and only requires a few steps.