I thought I could use my microsoft Office 2013 on three computers. I would like to use on two laptops and one desk top. Can you help me with that?

HUP permits the use on two computers;

http://www.microsofthup.com/hupau/faq.aspx?culture=en-AU

[Products, Licenses & Options]

On how many computers can I install the software?

2 computers, either 2 PCs or 2 Macs, specific to the software that was purchased.