Select an image in the application (open etc). Click the crop image and set the rectangle for the crop as it can be re-sized. You can set the PPI to 300 or 2 or 1 but in this case, set to 1 and then click apply. And you will see the image but now in squares.
Select the squared image and go to the edit menu and edit colors and adjust color balance and review ON and set the red and green etc sliders and click OK. You can move the sliders to change the color of the RGB channels as well as gray scale etc. Gray scale results in a very weird blurry effect that can be modified by changing black percentage slider.
You can turn it into a vector design by a number of ways, go to the object menu and create gradient mesh, though the result is more blurry than sharp which is not ideal. You can however then use the various color features to re-color the design.
You can also use the object menu and the other related command that turns a raster image (made of squares etc) into more squares / rectangles but on applying this, they are all vectors and you can ungroup them and then use the transform each command to randomly split the image apart as well as use rounding to create circular designs.
You can apply effects to it such as sketch category and bas relief etc and this will modify the image in a number of ways, you can use other filters such as glass etc to achieve similar modifications to the design.
The result can be copied to the library and then modified in Photoshop which has many raster effects that can be applied as well as image menu and adjustments to modify the squares. The creative cloud libraries are a great way to store all kinds of information in all apps in Adobe CC.
You can create unusual warping of the image by going to the object menu and envelope distort and warp and select bulge or one of the other warping presets or use the mesh warp though that works best by selecting points around the edge of the design.
Select an image and then go to the layers panel and right side menu and duplicate and then apply the crop image to that layer and set the PPI to 1 for that layer and press apply. You can also add different colors to the design via the edit menu color settings as well as perhaps warp the design via the object menu and envelope distort as well as use different opacity / blending modes for the top layer such as lighten to change how the mosaic layer interacts with the original unchanged layer.
You can duplicate the squared artwork using the art / option key and drag. You can then go to the properties panel and opacity and use blending modes such as darken etc to blend between that layer and the original to create all kinds of more unusual squares / rectangles
Select the squared (raster) design and go to the image trace, it is in the control bar at the top. Open the image trace panel (it is in the control bar also). Select different presets and you will see your design change radically if you go for 6 colors or shades of gray or line. Go for color mode and set the palette to full tone, limited etc and you will see a vast change in your design. The end result will be a vector design. Click the expand button and close the panel. You can now use the recolor artwork in the edit menu.
You can also use the object menu and ungroup. Once that has been done, select the individual parts and use the curvature tool etc to manipulate the design as well as add effects to it such as adding drop shadows or blurs to certain paths in the design. The result will be a very abstract artwork in most cases that does sort of bare some resemblance to the original imported or opened image but would be perfect for any floor of a Roman villa.