What is the best way to get them on? Thanks.

Position a molding onto the gutter, i.e., fit molding corner onto gutter corner at rear qtr window.
Starting at the corner, hook the top edge onto the gutter.
With closed fist, start at corner and firmly hit molding onto gutter. Some may use a rubber hammer.
Position front molding about windshield gutter.
Install by the same process.
Install corner piece.

Soak closed fist in ice water to relieve pain......j/k.