"He started working as an actor."
Translation:Il a commencé comme acteur.
Both commencer à and commencer de are used before a following infinitive. I asked MOD georgeoftruth when each is used and this is his response:
Hi ripcurlgirl. A lot of people use them interchangeably, only avoiding the "hiatus" of vowels whenever possible. For example, they don't say "commençer à ajouter" because of the double A's. I tend to follow this myself. However, TLFi gives a good distinction between the prepositions, and I sort of like it.
"Commencer à" is used if the following verb represents an action that has a development or an end goal. For example, commencer à devenir, commencer à comprendre, and commencer à s'inquiéter. There is more emphasis on the action itself as opposed to the action of "beginning."
On the other hand, "commencer de" is used for simpler actions with a duration, but not necessarily an end goal. For example, commencer de lire, commencer de courir, commencer de vivre. The emphasis there is more on "commencer" itself, the act of beginning an action instead of the actual action.
I know that both were on a document Sitesurf posted :