Learn French: Il nettoie la table avec l'éponge tout en chantant. - He cleans the table with the sponge while singing.

While both translate to "while singing", adding tout before the gerund (en + present participle) emphasizes that the two actions are happening at the exact same time. It strongly highlights the simultaneity of cleaning and singing.

How do we form the present participle chantant used in this structure?

You take the present tense nous form of the verb, drop the -ons, and add -ant. For chanter, nous chantons becomes chantant. This rule gives you the stem for nearly all French verbs when forming this structure.

I remember that the infinitive is nettoyer. Why is it spelled nettoie here?

Nettoyer is a stem-changing verb. For verbs ending in -oyer and -uyer, the y changes to an i whenever the ending is a silent e (like the -e in the il/elle form). This is why you see il nettoie but nous nettoyons.

Could tout en chantant go at the beginning of the sentence?