Learn Hardcore Polish: Pszczelarz używa dłuta pszczelarskiego.

Pszczelarz is the subject of the sentence, so it appears in the nominative singular form. It is a masculine noun meaning a male beekeeper. In this sentence, it is simply the dictionary form.

What does używa tell us grammatically?

Używa is the 3rd person singular present tense of używać. It means uses or sometimes is using, depending on context.

So:

ja używam = I use
ty używasz = you use
on/ona używa = he/she uses

Because the subject is pszczelarz = he / the beekeeper, używa is the correct form.

Why is it dłuta and not dłuto?

Because the verb używać normally takes the genitive case, not the accusative.

The basic form is dłuto. But after używać, it changes to dłuta.

So:

dłuto = nominative form
używa dłuta = uses a chisel / uses the hive tool

This is something learners often have to memorize: używać czegoś = to use something, where something is in the genitive.