Before-tax, Roth, and after-tax are separate decisions.
The RSP/401(k) SPD describes all three contribution types. Their tax treatment, matching eligibility, and withdrawal rules differ. It also describes Roth in-plan conversions and automatic conversion of eligible after-tax contributions. A conversion can create taxable income; it is not simply another name for a Roth payroll contribution.
Review: contribution elections, current limits, conversion settings, and how those choices fit with your taxable portfolio.