Learn German: Beim Entsaften trägt man am besten eine Schürze. - When juicing, it is best to wear an apron.

Beim is short for bei dem. In German, you can turn any infinitive verb into a neuter noun that represents the act of doing that action. When you do this, you must capitalize it. Using beim plus this capitalized verb is the standard way to say "while doing" or "when doing" something.

Why does the verb trägt come before the subject man?

This is the classic German V2 (verb-second) rule in action. The sentence starts with the phrase Beim Entsaften, which takes up the first position. The conjugated verb trägt must be in the second position, so the subject man gets pushed right after it to the third position.

How does am besten work here to mean "it is best to"?

am besten is the superlative form of gut (good), literally meaning "at the best". When combined with the general pronoun man (one/you), saying "one does something best" is the standard idiomatic way to give advice, translating smoothly to "it is best to do something".

Could I use the verb anhaben instead of tragen for wearing an apron?

Yes, you could say Beim Entsaften hat man am besten eine Schürze an. Both verbs mean "to wear" clothing. anhaben is a separable verb often preferred in casual, spoken German, while tragen is slightly more formal but perfectly natural in everyday speech too.