A grid is a structure of lines used by designers to help organise graphic elements (images ... should guide typography and page layout. In other words, design for the reader.

The grid serves as an armature on which a designer can organize text and images in a rational, easy to absorb manner. The less common printing term “reference grid,” is an unrelated system ...

It's a complete graphic design suite. But if you just need photo layout, it's highly recommended for exactly that. Canva offers a fabulous photo collage tool with hundreds of different grid-style ...