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Risk of buying stock
If you buy stock in established companies, it is vey unlikely that they will lose all their value. Spreading your money across multiple stocks -- diversifying -- reduces that risk because it is extremely unlikely that they all lose all their value at once. Spreading them across multiple industries and adding bonds to the mix increases diversification. Of course the trade-off is that if one of the stocks skyrockets you don't benefit as much as if you had been lucky enough to put all your money in that one stock.  You need to decide for yourself how much risk you are willing to tolerate in exchange for the chance of gains.  Other answers on this site have dealt with this in more detail.