A 401(k) is a tax-advantaged retirement plan funded with pre-tax contributions, reducing taxable income. The 2026 employee contribution limit is $24,500, with catch-up contributions for older workers. Prioritize building an emergency fund, then contribute enough to get the full employer match. Consider maxing out a Roth IRA if eligible, then increase 401(k) contributions. Long-term compounding can grow savings significantly.