Tap on the group symbol on the bottom:

Choose a group you're part of:

Select a route:

Select 'Navigate' and have fun...

Infuriatingly difficult to use interface.

THIS IS HOW I GOT A GROUP RIDE TO GIVE ME TURN BY TURN NAVIGATION (Note: you must have bought the 'Navigation NExt' version to do this.

If anyone else is having the same inabiliyy as me trying to just go to a gtoup , get a route, and then justnhave the app give youu turn-by-turn instructions (in the same way as a SatNav would........
Go to Route lab,
then Routes
then groups
then click on the named group (with your groups rides in it)
go to the blue 'page menu' - (right hand side of screen near top)
A blue sub-menu then opens up
then click routes (AGAIN !!!, but in this sub menu)
Go to your group, and it should have a list of rides.
Click on the ride name, and a map of the route should come up
then go to the blue 'page menu' (AGAIN!), but this time it has changed , and one of the options is 'USE'
Click on '+ use route'
THIS WILL PUT THE ROUTE FROM YOUR GROUP INTO YOUR ROUTES TAB

-TO FIND YOUR ROUTES NOW -
Go to the 1st menu, or just restart your app where it comes up with 'Good Afternoon'
Go to 'Route lab'
click on 'routes' button(3rd one down on the left)
You will now see all of your routes !!!!!!, and be able to go into them

-TO ACTUALLY ACTIVATE THE TURN BY TURN DIRECTIONS FOR THAT ROUTE, and actually seee tuen by turn navigation (the same as a SatNav):
Go to the 1st menu, or just restart your app where it comes up with 'Good Afternoon'
but this time click on the 'last route' button.

This has been a very exasperating afternoon to work this out ! , and not a great customer experience. Great app , confusing , very time confusing to work out interface'

If anyone has an easier way to do this, please let me know.