How many displays can I plug into MacBook Pro (13-inch, 2017, Two Thunderbolt 3 ports) In the MacBook technical specifications documentation, I read that it supports up to 2 monitors (or 1, it depends on display parameters). 

On Apple’s Thunderbolt 3  page, I read the same info but about a single Thunderbolt 3 port (of which I have 2). 

What is the number of monitors I can connect to my MacBook Pro?
You can plug in a maximum of two monitors

The technical specifications gives you detailed info about what your specific model’s capabilities are.  In this case, your model MacBook - 2017 13 inch MacBook Pro - has enough bandwidth to support two monitors at 4K or less or just one monitor at 5K.

The Thunderbolt information page gives you a generalized perspective of Thunderbolt’s capabilities.