I can help you with your 2nd question: livres, like many other words in french, can have multiple meanings.

In this context, it means pounds, a weight measure unit.

• Je pèse 200 livres. = I weigh 200 pounds

Livres can also mean Books, as you mentioned in you question.

• La bibliothèque contient beaucoup de livres. = The library contains many books.

It could also be the verb to deliver.

• Le facteur à livré mon colis aujourd’hui. = The mailman delivered my package today.

For your first question, I’m not certain I understand it. I will refine my answer if I can wrap my head around it.

Elle recueillait du doigt sur la table les miettes de son pain

That’s how you can break down the sentence in order to understand it :

• Il y avait des miettes de pain sur la table.
• De son doigt elle recueillait les miettes.

The issue here is to understand the use of prepositon de in the sentence.

De here means “by means of” / “with”. You could replace it with avec or à l’aide de but not with à.

There were multiple questions in your question and @Nickstoy answered the others.