1
The donkey is eating grass.
To sign this, you would first sign 'donkey' by flapping your hands at your temples. Then, sign 'eat' by bringing a squished 'O' hand to your mouth, followed by 'grass' by brushing the heel of an open hand up under your chin.
2
I saw a donkey at the farm.
Start by pointing to yourself for 'I', then sign 'see' using a 'V' handshape moving away from your eyes. Next, sign 'farm' by dragging your thumb across your chin, and finish with the sign for 'donkey'.
3
Donkeys are very stubborn.
Begin with the sign for 'donkey' to establish the subject. Then, sign 'stubborn' by placing your thumb on your temple and bending your fingers down into a fist, showing the animal's famous personality trait.