To see the scene, simply open your downloaded file in Blender.

Collections and Objects

In the Outliner, you'll see that everything in the file has been organised into Collections for performance and ease-of-use. The main scene is contained in the Dining Room Scene collection and is composed of collection instances of the various objects and props meaning you can move, rotate, and scale the props, but you can't edit meshes or materials.
To edit a particular prop, simply hide the Dining Room Scene collection, show the collection you want to edit, and you can now select and edit objects, meshes, and materials as normal, however, some collections contain other collections, like the glasses on this table, which cannot be edited from here:

You can move, rotate, and scale the glasses, but you can't enter edit mode or see the assigned materials. To edit them, simply find their collection in the outliner, show it if it is hidden, and edit the objects inside. 

If you're having trouble finding the appropriate collection in the outliner, simply:

1. Select the object in the viewport.
2. Open the Object tab of the Properties editor, and the collection's name can be found under Instancing.
3. You can now search for it in the outliner.
4. Show the collection if it is hidden and edit the objects inside.

Materials

Most of the materials in the scene are procedural and customizable. To make changes to a material simply select the object in the viewport, open the Shader Editor, and look for a node highlighted and titled Main Color.

Here you can change the principle color of the object

Select a different part of the model with a different material and repeat the steps

The bricks and wooden board materials are based on a main procedural texture node where you'll find all the controls for size and shape of the bricks/boards.

Floorboards texture node

Bricks texture node

Ceiling boards texture node

To use the scene, or props, in your own project:

• open your project
• click File -> Append
• browse to your downloaded file and click on it once
• click collection
• select the collections you want to import and click Append

You can now add collection instances to your scene with (Shift-A)Add -> Collection Instance -> the desired collection.