All Traffic reports combine your site's web traffic from all channels into single reports, there are 2 reports available in the All Traffic Section:
All Traffic Overview
The All Traffic Overview report gives you the highest level data of your web traffic, they include all traffic from all channels. You will be able to see various data like total number of sessions, conversions, duration, bounce rate, pages per session etc.
The All Traffic Channels report
The All Traffic Channels report will also give you data from all traffic sources but unlike All Traffic Overview, this report have them separate in different groups so you can compare performance from all traffic channel all at once. By switching between the chart tab, you will be able to visualize your data by a trend chart or a pie chart as well.
The image below is the pie chart available in All Traffic Channels report: