The Quick Compare page, which you can find under "Compare Analyses" in the left-hand navigation panel, gives you a side-by-side comparison of the organisms contained across a set of samples.
You can add or remove samples, scale and filter the data, and summarize the samples at different taxonomic rankings. Every comparison can also be exported as a spreadsheet or publication-quality image. The Shannon and Simpson alpha diversity statistics are also displayed below each analysis. Note that these are calculated at the selected taxonomic rank.
For more advanced options on comparing samples in One Codex, you can read more about Custom Plots, whole-genome clustering and analysis notebooks.