For this part, please see the administration tutorials here →
This tutorial is a good place to review → Hands-on: Taxonomic Profiling and Visualization of Metagenomic Data / Taxonomic Profiling and Visualization of Metagenomic Data / Microbiome
But for a simple stacked bargraph, you could also click into the Visualize icon (FAQ: Different dataset icons and their usage) and review the Charts tools there. Those take in tabular datasets. You could manipulate your reports in any way to you want to produce custom graphics (common manipulation tools are here Hands-on: Data Manipulation Olympics / Data Manipulation Olympics / Foundations of Data Science).