From a tax perspective, Betterment is no different from any other financial institution/brokerage. They will send you a 1099-B for your capital gains and losses, a 1099-DIV for your dividends, and a 1099-INT for your interest. All of this is taxable income and should be reported.
For retirement accounts such as IRAs and Roth IRAs, none of the above will happen. You would only report contributions and withdrawals from the account.