It's the first night Danny has to work. Because Jessie has a comedy act scheduled, Jessie is elected to be the babysitter for the night. And Danny trusts him to leave him in charge - even after the lousy job Jessie and Joey did in getting baby Michelle ready for bed.
The girls, knowing their father has left the building, takes advantage of Jessie's lack of babysitting knowledge. They trick him into letting them have ice cream in their room. And then when Jessie invites his band over the the house (four in all - two go uncredited), the girls get dressed and come downstairs - they even order a pizza!
When Danny comes home, there is a party going on with the band, the pizza boy, and the whole family - except for Michelle who's upstairs sleeping.
The episode is funny. The dialogue has some funny punch lines that make you smile or even laugh out loud. The fact that Jessie is so ignorant with kids just adds to the humor.
Danny's character always shows that he's a more serious, responsible guy. Having been newly widowed and having three children, Danny has had a chance to settle down. He's seen the more painful side of life which probably just adds to the reasons for his more serious role. But we'll see him loosen up...a bit...as Joey and Jessie work on him. We'll also see Joey and Jessie become more serious as time goes on.