What are these?

Sorry guys, can you help me here??

My sone has been given a collection of fishing things by a friend for his
recent birthday. A few of them I cnt explain to him.

They are...

A bag of polystyrene balls. What are they for and how do we use them?

Thats the easy ones...

A small packet containing about 2 -3 fet of nylon string. Looks like tooth
floss!, braided, white?!?!!

A green plastic moulding, about three inches square. It is flat and holds
two sets of plastic fingers, crooked in the middle. These are tiny, about 30
of them in each column spanning the green moulding. On the same moulding a
set of five plastic "strings", each with little bobles moulded on. These
are fine "strings", about 2mm dia.

A black plastic tree, three inches long. On one side a set of rings (same
size and shape as rubber float rings.
On the other side an equal number of pegs. It looks like the pegs go in the
holes...but apart from mindless fun, why?

David