To clean your meadows and boxes, you have to employ a groom. Go to the employee's section on your EC's page, then click hire a groom. Then when someone replys they will clean it and the cleanliness...
You dont neccisarily 'make' your own pasture on Howrse. You have to go to the 'Equestrian Centre' page and then go to the market from there.
From there you will see a tab labeled meadows. (Or...
First go into my equestrian center and click on meadows. If you want to put the meadow in pasture for the resident horses then click on the meadow and click Put in pasture for the resident horses....