Yes, in almost every case the photos, descriptions, facilities and star ratings come through automatically along with the rooms and prices, so you do not have to build a hotel library by hand.
The way it works is that a hotel supplier sends two kinds of information. One is the live part, meaning what rooms are free on your customer's dates and what they cost. The other is the standing information about the property itself, such as the address, the star rating, the room names, the facility list and the image gallery. Your portal keeps that standing information and shows it on the hotel page, which is why a property can appear on your site with a full write up and a set of photos without anyone on your team touching it.
Being honest about the limits, the quality of this content varies a great deal from one supplier to another and from one property to another. Big city chain hotels usually come with plenty of large images and a detailed description, while small guest houses can arrive with one poor photo and two lines of text. Descriptions are often only in English, and the same hotel coming from two different suppliers can carry different wording and different pictures, so what your customer sees depends on which source the room was taken from. Where you hold your own direct deals, you can normally upload your own images and write your own description instead.
It is worth opening a handful of properties in your best selling destinations on your own portal and comparing them with the hotel's own website, then telling your support contact about any pages that look thin so they can check what content options your plan allows.