There are many Hotel Software systems that you can buy to add to a Hotel site, most of which involve $$$$ and a learning curve to set up and use. Generally for a stand alone site the hassle and expense is not worth it.
Booking.com are a partner site who charge 15% of all sales (3% if driven through the Hotels own site) they are pretty much the biggest player around and are considered a must have for most independant hotels.
This is not free. Those websites use software and DB from a company and probably pay residuals to them. Unless you can get the money to pay for it you’re out of luck. Building it yourself wouldn’t be possible without a lot of start up money