What accounts would be affected and how by a transaction to purchase supplies for cash?

This is one of the simplest transactions you can do in accounting. Because you are 1. purchasing supplies and 2. you are using cash.

You already stated part of your answer in the question. The two accounts affected are 1. Cash and 2. Supplies

Because you are spending cash, cash will decrease (credited) and since you are receiving supplies, supplies will increase (debit). Remember both of these accounts are asset accounts and therefore both maintain a debit balance. To increase an asset you must debit it, to decrease it you must credit it.