Invest? meaning its money your willing to lose.... or save for your future?
If you want to save money for your future. Put it in a matched 401K associated with your job. Contribute your max each year, especially if your workplace matches it.
But dont stop there.... Open up a Roth IRA, protects your money for the future, much higher yield than putting it in a savings account, and with companies like Fidelity, you can start by putting in as little as 50 dollars a pay period.
By the time you ready to, send kids to college, retire... go on a kick ass vacation? whatever. Youll have the funds from your IRA without having to dip into you daily accounts.