When you click on MODX logo button it redirects you to MODX Manager and vice versa.
You can also set you custom manager path in options
If you are using MODX extra called Queeg http://modx.com/extras/package/queeg also you can easily open a resource for edititng just by one click and it provides additional information about resource when you hover icon.
More information for developers: https://github.com/bartholomej/modx-manager-switch