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When is complemented by a clause with an activity that 1) is a short interruption, 2) occurs at nearly the same time or shortly after another activity.   A nonprogressive verb form is commonly used (short duration).

While is complemented by a clause with an activity that occurs during or at the same time as another activity.   A progressive verb form is commonly used (longer duration). The while-clause can also indicate that a background activity is going on while the other activity occurs.

A comma separates the clauses to mark a change in word order – adverb clause occurs before main activity / clause.

No comma is used with standard word order – adverb clause occurs after first activity.

In traditional grammar, the adverbs when and while introduce adverbial clauses. They are called also called subordinating conjunctions which, in this case, join time-related clauses.  The clause is called a dependent clause. 

Note that in traditional grammar, a preposition requires an object, a noun or noun phrase, after it.  All other types of complements such as an adverb phrase, infinitive phrase, gerund phrase, or clause are not included in the definition of a prepositional phrase. The word is often called a conjunction or subordinating conjunction.  (In this website, the catch-all term is Connectors.) 
 

In linguistic description, the prepositions while, when, though, although, if, as if, as though, whenever, once and whilst may have as a complement: a finite clause, a nonfinite clause, or a verbless clause. The clause is supplemental (a dependent clause) (CaGEL 1262, 1267)  A large number of adverbs have been re-assigned to the category of preposition, which allows a wide range of complement type. See Prep Complements.  (CaGEL 700)