From your 'My Hub' page (please see below)
On the left hand side of your account, you will see the side menu where you can select 'workouts'.
You can then simply click 'Create Workout' at the bottom of your page
Enter your workout name and 'Create'
To search for a specific exercise use the search function on the right hand side of the screen.
Then simply select the '+' next to the exercise you would like in your workout.
You will then need to add all the important information in regards to parameters within each exercise which can be edited by simply selecting the different columns and entering the amounts, times etc.
Just remember to hit the 'Save Changes' button once finished!