I need to install conversion tracking on website

I ned to install conversion tracking on the website for a new hotel. I am the digital marketing manager for the agency employed by the hotel, but do not have the expertise to do this. I have tried to install google tags via tag manager and Google Analytics, but had no success. The hotel website is separate from the 'booking' section, which is run by a company called GuestLine. We need to be able to see how many people are getting onto Guestline via the hotel site, and where they are coming from