Open the MacHg preferences and select the Appearance tab.
Ensure the option "Show Branch Column" is checked.
Choose the menu item Repository > Add Revision Label...
Select the Branch tab
Enter the name of the new branch.
Switch to the History view.
Open the Labels panel at the bottom of the History view.
Click on the named branch you are interested in. (This shows the named branch in the history panel above.)
Either:
Control click on the named branch in the labels and choose the contextual menu Update Repository to Revision
Control click on shown revision in history panel above and choose the contextual menu Update Repository to Revision
Choose menu Update Repository to Revision... and choose the revision you have found through the labels panel.