Just start typing any 'string part' of the item you are looking for. As you are typing the items shown in the pull down will start to filter down. If there are thousands of items in the pull down, there might be a slight delay.
The intelisense is case insensitive, and any part of the string will do (so you do not have to start typing the start of the string). Deleting the your typed charactes will remove the filter.
The following figure shows how different strings result in different results:
Intellisense is also used for the input field of filters. Using these filters in a list box it is very simple to find the items you want. Just select the Filter for the specific column and start typing.