Order hash is generated when creating an item or putting it on sale. Use that hash in this field.
See state Order Hash
If you don't know the hash, you can get it using the API, for example Get Order Activities will return all activities (BID, LIST), everyone has a Hash.
For example, we do it in Buy item demo page to find the sell order hash.
Field Type - Number
Amount of items to buy, more than 1 is possible for ERC1155 tokens only.
Depending on the fill Type selected, these events will be triggered: