Roth type contributions are taxed at the time of deduction from your pay (unlike traditional tax-deferred 401(k) contributions). Then when you take it out at retirement you won’t get taxed on the investment growth. It is designed as an incentive to invest in retirement early.
The Tag 401(k) Plan allows both traditional pre-tax 401(k) (tax-deferred) contributions as well as Roth 401(k) contributions at the same time. Both types of contributions will be housed in one TAG 401(k) Plan account together. It does not require a new account separate account for this. Vanguard tracks the origin of the contributions and keeps records of growth to both types in the account. Roth 401(k) contributions can be set up using the long format enrollment form.