Pour vinegar into the small plastic bottle (use a funnel if necessary)

Pre-stretch the balloon by inflating and deflating

Use a small, clean dry funnel to put the baking soda into the balloon

Carefully put the end of the balloon (while keeping the baking soda inside the balloon) over the top of the bottle

While holding onto the bottle, empty the baking soda from the balloon into the bottle

A chemical reaction occurs and the resulting gas should inflate your balloon.