I don't have 401K yet because I've been working for this company for less than 1 year.
My wife has 401K account and she has about $10,000 in it.
You can use the money to buy some types of funds.
Last year she bought some VANGUARD funds.
Because the stock market is US was very strong last year.
Her money in 401K went up by 30%.
BUT!!!!!!!-------------------------------
If the stock market crashes, like what happened in 2008. You have a big problem .
So 401K is like a portofolio. You can have cash or stock or bond in it.
But you won't be able to spend the money ultil you are old enough.
from wiki:
401k基金规模
401k退休福利计划,是美国于1981年创立一种延后课税的退休金帐户计划,美国ZF将相关规定明订在国税法第401K条中,故简称为401K计划。美国的退休计划有许多类,像公务员、大学职员是根据其法例供应退休金,而401K只应用于私人公司。
计划是自愿性质,劳工可依其个人需求自由选择ZF核准过的的个人退休金计划。内容为要求雇员定期拨金钱至个人的退休计划,同时公司将拨部分资金至每位雇员的401K,直到雇员离职。而雇员可自行决定拨钱的数目多寡。