get into the garden is the first listed Mission on the To-do List, the mission involves getting into The Garden.
How to complete[]
If the Untitled Goose grabs the Radio that can be found on top two sacks of (presumably) dirt, the Groundskeeper will notice and open the door to The Garden, then the Untitled Goose can enter.
It's also completable if the Untitled Goose turns on the sprinkler because if the goose does so, the Groundskeeper will go out and turn it off, this will make it possible for the Untitled Goose to enter The Garden.
get into the garden · get the groundskeeper wet · steal the groundskeeper's keys · make the groundskeeper wear his sun hat · rake in the lake · have a picnic · make the groundskeeper hammer his thumb
break the broom · trap the boy in the phone booth · make the boy wear the wrong glasses · make someone buy back their own stuff · get on t.v. · go shopping · trap the shopkeeper in the garage