The Monstree dataset is known to work, so there should be no errors or problems during the reconstruction. This might be different when using your own image dataset.
Import the images in Meshroom by dropping them in the Images pane. There are different folders in the Monstree dataset: full (all images), mini6 (6 images) and mini3 (3 images) to test out.
You can preview selected images in the Image Viewer pane. To display the image metadata click the (i) icon in the bottom right corner. For images with embedded GPS information an additional openstreetmap frame will be displayed.
In the Graph Editor you can see the ready-to-use default pipeline.
The Graph Editor contains the processing nodes of your pipeline. For this project you do not need to change anything! In fact, for many projects the default pipeline delivers good results
You can zoom in or restructure the nodes. You can hold Shift to pan using the mouse. To insert new nodes right-click in the Graph Editor pane. For the Graph Editor use the buttons on the bottom left side of the pane to (re)order.
Before you start the reconstruction, save the project to the Monstree folder. (File ? Save as) (The HDD should have enough free space.)