TSA is a transportation plan, the money is taken from your pre-tax salary. Health FSA sets money on the side for things like small medical expenses, however if you don’t use it there is a chance to lose your money. 401k is an investment account, a tax deferred account until you take your money out. Some employers also offer matching percentage of the money you invest. But there is always a risk of loosing money so you must read to make sure you know where you are putting your money.